The twisting hanging knee raise hits the lower abs and obliques. You can hang off literally anything that will hold your weight for this exercise. Most people will hang from a pull up bar. Hang off the with a slightly wider than shoulder width grip.
Once you’re hanging with your feet slightly off the floor, pull your knees up and across to the left side of your body.
Pause, then slowly lower them back down.
Now raise your knees up and across to the right hand side of your body.