barbell squats. altough you mostly work your legs, your core will work a lot as well.
for abs just to cable crunches
Discussion
good inspiration.
Is there a way to engage core even more during squats?
there is no trick to it. dont use a belt so you need your core for stability. use enough weight but dont hurt your spine. if you can barely do 3x 10 reps then the weight is optimal and you will get stronger. keep increasing the weight by only a bit everytime you feel like you got stronger. but I am sure you have heard of progressive overload. 😃