When asking about arrangements we usually use the present continuous:
- Are you working tonight?
When asking people to make a decision about something in the future we use will:
- Will you work tonight?
Example (2) makes it sound as if the listener has a choice over whether they will work. It might be understood as a request by the speaker asking them to work. It depends on the context.
When asking about how someone is going to be spending their time, or when asking what activity someone will be doing at a particular point, we use will be doing. i.e. the future continuous:
- Will you be working this evening?
Example (3) is asking whether the OP is going to be spending their time working this evening.
Given the wording of the Original Poster's question, it seems that the most suitable form for their particular query would be (1). Notice that this is the form that the Original Poster actually used in their question:
Let's suppose I'm gonna ask my colleague whether he or she is working this evening ...