Auto point on the selected layer

If you have positioned a 3D layer outside of the camera view and you have a one-node camera, you can use a vector math expression to point the camera at the layer by using lookAt(fromPoint, toPoint). If you have a two-node camera, you can reveal the camera's point of interest by pressing the A key, then reveal the Position property of the layer you want to look at, then show the Parent/Link column (Shift + F4) and drag the pickwhip from the Camera's point of interest to the target layer's position.

Another option would be to use an expression to point the camera at a 3D null, then Shift + Parent the null to any 3D layer, then release the Parent to get the camera to point at the 3D layer.

There is no automated way to get a camera to point to a 3D layer without an expression or without resetting the camera and the 3D layer's position. Using the Shift + Parent then release is the closest thing I can think of to get a camera to point at another layer. I use a null on the Point of Interest or as a lookAt target all the time.

Here are the expressions:

// For a 2-Node camera Point of interest
thisComp.layer("3D Null").transform.position

// For a one node camera orientation
lookAt(position, thisComp.layer("3D Null").position)

All you have to do is make the Null 3D and name it 3D Null for this to work. I use both all the time.