Hi Pilou - the Join command knows how to join curves together into larger composite curves or surfaces together into multi-face or solid objects. There is no functionality in Join for joining a point to anything else.

I guess you want to have a kind of "Persistent point on curve" - a point that is located at a particular parameter value of a curve and moves with the curve when you edit it? MoI does not currently have anything set up for that.

- Michael