I seem to have permanent lines on the palms of my hands from playing Super Nintendo & similar years ago. I think I was supposed to use my index fingers for the buttons on the top of the controller but I used my thumbs which involved bending them way back.
Alrighty, most of the details have been figured out, so here’s the whole picture:
I am currently interning at a company that produces digital calculus textbooks. As I said earlier, none of the interesting visual details could possibly have any relevance to this occupation, but…
…the two objects in my pockets are a cell phone and an authentic Leatherman, which I have because I have done (and will continue to do) stagecraft / technical theater for much of my adult life. This explains the scar on my left hand, which is actually from a hot glue gun. This also explains the paint and tape on the jeans, and CandidGamera was right on the money when he posited that I don’t replace the dirty jeans because I like the look.
…I also don’t replace the jeans because I just DGAF about what people think of me, which also explains the nasty-looking stubble and the unusual phrases.
…I am indeed a musician; a guitarist, to be precise. “Takadinagah” is a method of counting quintuplets (one pulse broken into five equally-spaced notes), which is a very non-intuitive rhythm that requires a good amount of practice before it can be performed naturally. I have a somewhat unorthodox method of playing guitar: instead of using a pick, I pinch my thumb and index finger as though I were holding a pick and then use the index nail as the downstroke and the bottom of the index for the upstroke. This causes the callous/dead skin on the tip, and occasionally a string will get caught underneath the nail, which causes the white part to start much earlier.
…I used to work as a character performer at Walt Disney World. The character I portrayed most often was Tigger, which is why I got the sweatshirt, and which is why to this day I find myself bouncing around instead of standing still like a normal person.
…the dead skin on the palms is caused not by rope burn, but by lifting weights.
…lastly, the one that no one came close to figuring out: the head injuries are not occupation-related in any way. They are patches of mat burn from doing Brazilian Jiu-Jitsu at the gym. Even after a win, I’ll find myself with mat burn in lots of different places, including the top of my foot, my elbows, and my shoulders – but those are always covered up by clothing, making the head injuries even more mysterious.
If he caught be before my after-work shower, the metallic dust around my fingernails, and the general grime on my hands and face would be a good clue I’m a metal worker of some kind.
Otherwise, he’d have to spot minute markings on my hands, and whatever metal dust managed to cling (It’s persistent stuff, I’ll grant. For a while, I was literally sneezing silver).
If he scanned me right now, Mr. Holmes might notice that I’m wearing bright red coverall that say “Rockhopper Petroleum” on them. This might give him a subtle hint as to what I’m doing. And the fact that he’d be on an oil rig off the Falkland Islands might supply supporting information.
He would need some more info to determine your profession, are you currently ;
Shouting at someone - company man
Checking the rousties doing the casing tally at night - night company man
Drinking coffee in the mudloggers shack in remarkably clean coveralls - professional pebble counter 
Good luck down there.
Like another poster, I’m a driver. If you ever encounter a guy with a potbelly, dark left forearm and shoulder problems, its probably a bus driver. Long hours sitting in the same position, rrpeatedly turning a steering wheel.
Female bus drivers can be identified by their crows feet, prodigious facial hair and shrill, nasal laugh…possibly a mating call of some sort. Yeah not a lot of cute lady drivers out there.
Crippled guy, with a holier than thou attitude? Might be a light rail operator. I tried out for the gig, wasnt detail oriented enough for such a tedious job. But.i can sense one a mile away.
Tea with milk. Which would tell Mr. Holmes my nationality as well.
Or a dancer.
Or a ‘dancer’.
Anyway, Holmes would be unable to do much with me for the same reasons he’d be unable to do much with engineer_comp_geek or any of the other technical professions these days: Computer work just doesn’t require much in the way of special tools other than the computer, and doesn’t leave much in the way of tell-tales except, perhaps, extra weight.
I do, however, have a few red herrings: I keep my hair extremely close-cropped, anywhere from shaved down to stubble to just barely fuzzy. I have a pair of faint scars, one on nearly the same location of each pinky finger. I have a very visible red mark on one side of my head, but no associated swelling and no apparent pain.
None of those are relevant in the slightest. My hair is short because I like short hair and don’t like dandruff. The scars are mysteries; I’ve had them since early childhood and have no idea how I got them. My red mark is a port wine stain, which is a congenital vascular defect which has never influenced my life in the slightest. (Admittedly, the fact I’m not vain enough to care about or, on most days, even remember a large discoloration on the side of my head can rule out some professions, at least using the level of reasoning Holmes usually showed, but it is not really probative into what I do.)
Weightlifting! Tch. I should have considered that, but - blisters? You may be overtraining. 
When I thought about the musician thing, it made me wonder about the finger, with regard to stringed, plucked instruments - but I thought most people used a pick or a thumbnail, not the nail of the index finger, so I considered it unlikely.
I don’t train very hard or very often (3-4 times per week), but I have fairly dry skin and I don’t wear gloves, so… yeah. In any case, it’s never painful, I just pick off the dead skin and get back to work 
I had hoped that you were a fellow tabla player 
“Takadinagah” could be parts of the rhythmic speaking patterns, the callous on you index finger from playing the sound “na”, and the dead skin on your hands from tightening the skin on the drums. I couldn’t figure out why your nail would look strange, though.
Impressive. I am indeed a grad student.