What do I think about Khadgar. Reckless, headstrong, slow to accept advice, some of what all we heard in the canon, right? But besides. Brave, intelligent, good-natured, clever and fair.
I also think that Khadgar wasn’t quiet assiduous bookworm. (As for the movie i think where was just not enough of time to show all sides of his nature, so he could seem clumsy and it’s very strange, frightened and bookworm). He says that knowledge is power. He spent a lot of time studying the magic. But this is not the same thing as being bookworm, boring nerd, e.t.c. He is just inquisitive, curious and wanted to be a really good mage. As for the fact that Khadgar is curious and even a little mischievous it is known from the canon (game/books canon I mean). He was spied on his mentors and I knew all their dirty secrets. Because of this reason he was chosen to being sent to the Karazhan for spying on Medivh.
I think he cared about Medivh and protected him. But it’s also canon. I’ve quoted these things. In addition, Medivh asked him for protection. It’s also canon. Just find this quote here or better read the book. I like it much better than any “comics books and novelizations of the movie”.
I told that some speculation that “Khadgar is capable of any, even abusive conditions to get the power from Medivh” is bullshit? And now we have “Harbingers - Khadgar” video, where Khadgar renounces that power (yes, in fact it was not that kind of power, it was a trap created by Dreadlord, but anyway) even in more pleasant circumstances. So, it’s also canon.