DOC = diesel oxidiation catylist, first thing in the exhaust pipe, dont think new kit has them anymore but could be wrong, fitted on land rovers from 300tdi onwards, early td5 (Euro2) didnt have them, later ones (Euro3) did.
DPF = diesel particualte filter, this is the one that needs cleaning, from 07 (Euro4) onwards
I think Euro5 was basically Euro4 plus stop/start?
SCR = cat this is the one that transforms the nox using adblue, 2016 (Euro6) onwards, for trucks Euro6 came out in 2014 and has been nothing but a pita ever since.