So what I usually do is compile a list of melodic hooks from popular songs my students enjoy. Every so often, we’ll play them and let the student try to pick them out on the piano or their instrument of choice. I find that the satisfaction they get from being able to recreate a familiar pop‑culture melody really helps spark their interest in getting better at playing by ear, which in turn motivates them to stick with the exercises.

Shameless plug but I built a unique game specifically to help some of my more classically trained friends get better at playing piano by ear.

It's a free piano game in the style of the old "Simon" toy which presents players with increasingly longer sequences of musical notes and challenges them to reproduce the sequence using either an on-screen piano or connected MIDI keyboard. It also works with acoustic instruments through the mic.

https://lend-me-your-ears.specr.net