Would 'Sunuş ne zaman başlıyor?' also be alright or does the word 'Sunuş' refer to something different?
This is a great question. sunum refers to a physical thing that you a presenting (a report, an essay, etc.). They are often paired with Powerpoints.
sunuş refers specifically to the style in which something is presented. (Like "his presentation of the fact was not satisfactory). The first is more concrete and the second is more abstract.
Exactly! You can't really asked when one's presentation style will be starting. :)
sunma is the gerund form of the verb sunmak but it is not normally used to mean presentation. That may be the reason.