I like to cum at the end of the session but it's not a requirement. I already had very good sessions without cum at the end, and low quality sessions with cum may happen too. It's like cherry on the cake for me: it only improves the quality session a little bit but it's not compulsory. And I would never ask her to do it, it's up to her to decide how she wants to end the session.

However, if it is a session with cum at the end, I much prefer to do it myself than letting the dominatrix do it. I'm generally more efficient than her (unless she uses a milking machine), and, most importantly, I love when she tortures me at the same time and it's easier for her to torture me if she has both hands free.

And thus I much like when she orders me to "do the work" myself while she sadistically and increasingly tortures me, implying that she will stop only when I cum.
The most common situation is her sitting on my face and hardly torturing my nipples while I try to finish myself (which is ALWAYS very arousing and therefore very successful), but she may also handsmother me, headscissor me, torture me with electricity or anything else...