I have created several circles and points on a sketch and I would like to constrain in an assembly of other parts in relation to the circles and points of this sketch. Currently I can't choose the objects of the sketch while I can choose the neutral fiber of the cylindrical part to constrain.
As you @benoit said, it is quite possible in an assembly to select a sketch entity included in a part in order to constrain it with an entity (face, edge, sketch...) of another part. Your sketch of the part must be visible.