The hanging knee raise is an easy exercise to start with. All you need is a high bar, you can hang on. It is important to keep the motion slow and controlled. In that way the knee raise is an effective workout to train you abs and core muscles. This is also a good preparation for advanced moves like the front lever.
Once you can do many controlled reps of the knee raise, it’s time to try the hanging leg raise with straight legs.
Hanging knee raise variation
You can also try the twisting hanging knee raise to target other muscles like your side abs.