The expression is right and it is an expression that defines a definite opinion. The expression states that you are sure about someone and them being interested in a certain position and that you are not guessing about the other person's intention or desire for a certain position.
I like the answer given by rankin34. Another option is to simply state, I know someone who would be interested in that position. (You do not need the in working in part because it is already understood that it is an employment position.)