The first two sound natural, except for one minor error in example 2, in different settings.
What's in it for me?
You hear this often in books, TV and movies. It is idiomatic but it sounds selfish. It is what a person might say if they are in no way interested in how something benefits the other person.
What do I get out
if of it.
(note correction to your quote). This also sounds pretty self-centred, although arguably it is a little softer than the previous example and perhaps acknowledges what the other person gets out of it.
Your 3rd and 4th examples seem like attempts at a more formal approach, but neither are idiomatic.
You might ask:
How do I benefit?
How do I profit from this?
How do I gain from this?
Note that asking "how do I" has a slightly different inference from "how can I". The former suggests that you understand how the business works but fail to see where any profit falls to you, whereas the latter implies that you don't understand how the business works.
A more polite way of asking the same thing may be:
Can you tell me how/where I fit into this?