What do you mean I can do it?

I can do it means: I will do it; I can do it.

Second, relevant examples:

1. There is nothing I can do. I'm just a nobody here.

I can't do anything. I am just a pawn here.

I think I can have another piece.

I want to know what I can do to improve my grades.

I don't know how to improve my academic performance.

George only needs a little pocket money.

George has little change to get by.

No secular ruler can do whatever he wants.

No king in the world can do whatever he wants.

6. This work is not urgent; We can do it tomorrow.

The work is not urgent, we can do it tomorrow.