I stumble over this problem! I have a cam (axis) that has a vertical vouvement. I have a pebble that is guided horizontally. How to manage the movement of the roller on the cam knowing that solidworks refuses the "cam" constraint because it does not have a closed contour?
Either you draw a template part (here in blue) for the cam path (you need a closed outline for it to work I think) and you hide (or not the part in the assembly see attached image, or you make a trajectory constraint following Azrod's advice.
The 2 work, it's up to you to see which solution you prefer.
For the point normal to the trajectory, draw your trajectory in the center of your axis (trajectory // to the real trajectory and the no worries)
Edit: the disadvantage of this method if I'm not mistaken is that your point in the center of the pebble and your trajectory must be on the same plane and this can sometimes be restrictive.