I'm having trouble reading several dimensions on this technical drawing.
Figure 1. The cylinder is 24 mm diameter with an outer thread of M24 x 2 (pitch) extending to 16 mm from the end.
And what is the diameter of the rotor? Is it 40? if yes then why they didn't put any diamater mark next to the number 40?
Yes, 40 mm. It should be marked with a Ø symbol or "DIA".
And I cannot find out the angle of the central key relative to slots?
It's not there in the extract you have given. I would assume 45° - but that could be an expensive assumption.