Below you will find a video of an excellent basic drill for isolating and developing elbow attacks and counter attacks.
Training partner is positioned with his back to the wall in order to minimize his retreat to the rear and thus maximizing training time and elbow volume. Despite the protection on the head of the training partner and elbow protection of the feeder, keep it light and happy, as elbows are like hammers and can cause lots of damage.
There are many different layers of the drill possible. At first, the receiver (training partner on the wall) could just throw punches without much regards for defense and allow the feeder (the elbow guy) to get comfortable to slip in and attack with elbow combos in different planes, as well as off balancing and trapping movements. The receiver could start with just head shots, then progress to head and body shots, then add kicks or isolate any of the above.
Then the receiver should start making things much more difficult for the feeder or even become the feeder himself — being a feeder is a term from Sayoc Kali and it means controlling the tempo, flow and the outcome of the drill. So the partner on the wall can start moving laterally, defend against the elbow attacks, tie the elbow guy up in close and make his life otherwise uncomfortable and his objective more difficult to achieve, which in turn stimulates the elbow guy to launch and follow through better elbow attacks and counters.
The elbow guy could also begin spicing things up and add complexity to the exercise, depending on the training objective. For example, while still setting up elbow strikes from all angles, he can focus more on trapping and off balancing, as well as clinching and simply do not leave once he enters, choking his partners ability to throw effective punches. Or he can snag an arm or two on the way back out and perform arm and wrist locks. Or he can finish with a takedown. Or he can add other tools, such as finger jabs, slaps, punches of his own, as well as knees and kicks. It all depends on the objective and what kind of a game or an aspect of the game are you trying to develop.
Have fun with this and be safe!