Is there any function which gives a pointer to the entity on a known position?

I mean some function like this (which is not existing)?
you = entity_on_this_position(vector(0,50,0);

c_scan

c_scan would be a solution but is there any faster function?

No. (You could iterate over all entities and check if the position intersects their bounding boxes but that would be slower than c_scan.)

c_scan would be plenty fast if you use a very small scan radius and cone, and employ all the IGNORE_WHATEVERS as you can. If you know the exact location and the exact entity type, you could narrow it down enough so that c_scan is very fast.

Ok thanks than i'll have to use c_scan.

or...

a) using nodes to store what is at each position

b) use ent_next to cycle through the entities to see if any are