A 2 year old taking his diaper off is normal and a very common thing that happens.
One reason that your 2 year old takes his diaper off is likely because your 2 year old hates wearing the diaper or hates wearing the diaper once he soils the diaper or wets the diaper.
He could be taking it off because he hates the feeling of wearing the diaper once he pees or poops in it.
If so you might need to change him more often and use pants on him that make it harder for him to get his diaper off.
If your 2 year old can't access his diaper then he cannot take it off.
It could also mean that your 2 year old is done with diapers and wants to potty train so if your 2 year old is taking off his diaper when it's wet or when it's dry then try taking him to the toilet and see if he's ready to use the potty instead.
It doesn't always mean your 2 year old is ready to use the toilet when they take off their diaper but sometimes it does mean that.
If he's not ready to use the toilet then you must explain to him that he must wear the diaper unless he uses the toilet.