Why does quoi come before prendre?
Why not "Je ne sais pas quoi avoir pour le dessert" ???
Lequel means "which" -- and that would require there to be a specific choice between 2+ choices. "What" here is just referring to any old possible dessert options.
Why not 'je ne sais quoi'?
I'm sure I've seen this before.
What is wrong with je ne sais pas LEQUEL ...
What's wrong with "je ne sais pas quesque je veux manger pour dessert" Is it correct french but a wrong translation?
First of all "quesque" doesn't exist in French. Maybe you meant "qu'est-ce que", which is interrogative and would be wrong here. "Je ne sais pas ce que je veux manger" would be correct, but not really a literal translation of the English sentence.
je ne sais pas ce que d'avoir pour le dessert. Rejected. Reported.