All depends on Lapras's move pool and/or usage then.
If Lapras has a lot of decent special moves, Sp.Att and Speed, but if you prefer using Lapras as a wall, either focus on Def and HP, Sp.Def and HP or Sp.Def and Def. I prefer (Sp)def + HP. You just check which opponents Lapras is going to have to block (Mostly Electivire), in this case Electric pokemon, most trainers have an Attack-based electrivire using thunder punch (They only focus on one own type move for STAB), thus you should EV train Def and HP.