My most marketable skills are business knowledge and designing efficient processes. I could likely make a decent living as a businessman as far back as their have been businesses, within the confines of language knowledge.
“Build a microscope” is a monstrous task before people had microscopes. It’s immensely, immensely difficult to do that.
In any case, microscopes predated an understanding of the role of germs in disease by an awfully long time. One did not instantly result in the other.
Well, that’s kind of my point. The time-traveller from 2115 has provided you with information that is of no value. The idea that dark matter is composed of a WIMP is already on the table so unless our intrepid time traveller knows how to prove it with 2015 technology, or knows what you can do with the word “Lemurino” that’ll make money, what good is he? He sounds like he might be able to serve coffee in a Starbucks, but you’ll have to teach him how to use the espresso machine.
I don’t think the OP is about “What do you know that people in the past didn’t.” I am a doofus, but obviously I know an uncountable number of things people in, say, 1816 did not know. But the question was how RELEVANT are you? What skills do you have? Knowing about continental drift, radiation, and germs causing disease is interesting but you need the skills and the savoir faire to put those into practice, and in some cases underlying technology; an understanding of the existence of radiation in 1816 is effectively worthless.
My education is in math and physics, so I think I could make a go at it in any civilized place. I can also juggle, if that technical stuff doesn’t work out so well. 
I wouldn’t worry about the language. in Europe, I could learn Latin quickly enough that I’d be able to communicate with the educated classes. Orce-fay equals-hay ass-may imes-tay acceleration-hay!
I taught sailing professionally so I think those skills could carry me back to the earliest seafaring societies.
A microscope can be just a single convex lens and a mechanical holder (that’s what van Leeuwenhoek used), though a 2-lens design works better. To make a lens, all you need is a piece of transparent material (usually glass) and something to polish it with. It’s a lot easier than pencil, which requires a very specific mineral (graphite).
As a politician I’d could probably go back to the era of Machiavelli who has taught me more than a few things!
I help run some IT infrastructure projects projects for local government.
You’d probably find loads of people like me working on stuff like the pyramids: bureaucrats skilled in civil engineering projects.
My experience in military engineering from 20 years ago might have some benefits too.
In Poul Anderson’s “The Man Who Came Early,” the traveler from the 20th century is mostly frustrated and mocked for his inability to do much of anything with his engineering knowledge, in the 10th century.