No sentence with "gonna" is natural.
Do you by any chance know how much my boss is going to increase my salary? - ok
Do you by any chance know how much my boss is going to raise my salary by? - ok
In line with a comment above, "give me" is informal.
You mix "gonna" which is informal in the extreme with the very formal "increase my salary".
While the expressions are natural enough, the mix of formal and infomral sounds strange.
raise is both a noun and a verb.
I'd go more for
How much of a raise is my boss going to give me? (I had to shift "is" as well.)
As aslo stated above, in many places only your boss and you discuss your salary, so the conversation is not exactly natural. :)