-
Can apes be tickled?
-
What is the purpose of the ridges on top of a dog’s mouth? (Grip?)
Any animal can be tickled. I think you mean: do they react to tickling similarly to the way humans do. 
The answer is “yes”, at least for great apes. One of the common requests apes make when they’re taught sign language is to be tickled. And they react similarly to humans. Young chimps can often be observed playing a game of tickle in the wild.
Not sure about the lesser apes, though.
My ‘WAG’ would be that the ridges help to increase surface area, which helps when dogs are panting to cool down.
We have ridges on the roof of our mouths too. They’re called rugae.
Can’t answer the first one, but the answer to the second is obvious: To hold peanut butter! 