"Tapadh leibh Ollaimh!"
Translation:Thank you, Professor!
It is funny because I don't think I have seen much about the rules of capitalisation. It seems like it is are mostly the same as in English. Proper names of people or places (Iain or Alba), even Albannach -Scottish is capitalized. I assume that you are asking because Dualingo has capitalized Ollaimh here (but not thidsear elsewhere). In this case I believe it is capitalized as you are directly adressing the professor.