So basically i cant collect any skulls while playing Halo 3 on the master chief collection on my xbox one … i can see the skulls but i cant pick them up or earn the achievements …can anyone help 
so you go up to them and press X and nothing happens? or is it that you can pick them up but the achievement won’t pop?
what difficulty are you playing on? play at least on normal for achievements to pop.
Check your controller layout and see what your reload/action button is. Mine by default is RB.