I have a question about a game library and there's a guy named Gama11 who has contributed to the library. He generally answers my question about the library. As I say I have a question but I don't know how to ask him to answer my question. Perhaps I just need to wait for a while until he find my question.
This is not how Stack Exchange works, or is supposed to work. The system is set up to focus on the posts, not the users.
If the question can only be answered by the author of the library, then you should see the web page of the library; they probably have a forum, a mailing list or an area for bug reports and/or feature requests.
If the question is fit for Stack Exchange, then it shouldn't really matter who answers it.
Obviously the author of a library would likely be the most knowledgeable person and an answer from them would be ideal. But if someone else has the right answer to your question - then what really matters is that you got your answer, not who provided it.
Stack Exchange deliberately doesn't provide much in the way of directly contacting users. Some high-rep users would be drowned in personal requests.