Question

Which is Bilbo’s struggle to understand who he is.

Answer 1

Really all of them, but if you think about it, it will be Bilbo and the dwarves. The dwarves were constantly with him, and he had arguments with many of them, but while spending time with them, he was able to find out that he had an adventorous spirit, and that he was no ordinary hobbit. 

With gollum, he didn't really try to find out what he did, he just made a bunch of riddles, found the ring, and left him

With the dragon, he also just did a bunch of riddles too, so Bilbo and the dwarves is the best answer.

PS the dragon is called Smaug

hope this helps