can't select docking clamp to dock with

[jwenting]

Can (using some help from mechjeb) get 2 craft close enough for docking (100m or so) but for the life of me I can't target the docking clamp on the target ship before it zips away into the wild blue yonder.

Even at 100m separation, it's just too small for the docking port to be clickable...

[Nibb31]

You don't need to target the docking clamp of the target ship. You just need them to touch.

If the target ship is just zipping by, then you haven't yet reduced the relative speed of the two ships. You have to set the other ship as a target (you can do that in map view). Then, make sure your nav ball is in Target mode, point your ship towards the yellow retrograde marker, and burn until the velocity is 0.0m/s. This is rendezvous.

Then you can proceed with docking by just pointing both ships in the appropriate direction, switching on ASAS on both ships, and just translate towards the target with IJKLHN (don't use the WASD keys). If you start going to fast or you find yourself moving away from the target, cut your relative speed to 0.0 again, as described above.