Selecting 2D source point in 3D camera tracker

Welcome 😊

Hi! In 2D Source mode, the points are just raw tracking data and not part of the 3D solve, so you can't create a null directly from them. To use those points, switch back to the "3D Solved" mode, find the corresponding points that best match the motion you want, and then right-click to create a null or solid. Unfortunately, 2D Source points can't be used to generate scene elements directly.

After setting an origin and ground plane, then using the same Target to add a camera and a solid so you can verify that you have a good camera track, try this workflow:

Pick any single camera track point that is sticking to some detail in the shot for more than a few frames. Add a solid so you can see it move because you can't see nulls. You'll get a very small square 3D solid. Verify that the point you selected has good data and it sticks to the surface. Make the new 3D Layer a Guide Layer so it doesn't accidentally show up in the render. Add another small 2D solid to the comp, make it a Guide layer, and apply this expression to Position:

L = thisComp.layer("3D layer");
L.toComp([0,0,0]);

As long as the layer name matches your 3D track point, you'll have a 2D layer that follows that single track point you created.

If the single track point had good data, or you have selected three or more points and have a good track, the 2D layer will be attached to the 3D track solid (or null).

I use this workflow all the time and have saved the expression as an animation preset so I can attach a 2D null to any 3D layer below it by changing the expression to use the layer index like this:

L = thisComp.layer(index + 1);
L.toComp([0,0,0])

 One of the more common uses is to attach a null to a shape layer stroked path as a pointer for a graphic by using the Create Nulls From Paths/Points follow Nulls script available in the Window menu. 

Only the 3D solved points have 3D information (XYZ). All 2D tracking points of the 2D source with bad tracking information or different movements (moving objects, reflections etc.) are killed automatically by the algorithm. That's the downside of this very basic/easy-to-use Camera Tracker. In my opinion, the Camera Tracker needs an advanced option to manually track points, give them waits and constraints (distance, planar surfaces etc.) and have a good export/import options. I write this for years but Adobe does not listen!

I have the same problem. 2D source fits well but can't use right click on the points. What's the point of 2D source if we can't use them?

I'm really hoping to find a resolution to this problem as it will open up so many creative opportunities.

It's rediculous, but I'm half tempted to screen record the preview screen with the 2D source points in order to then retrack them through the Track Motion function so I can create nulls based of the position.