dsmash: all sorts of things, as a lucario who tries this and gets shielded made a mistake by doing dsmash in the first place.
Usmash: Lots of things after the initial frame, there's a weird time in the attack where it cancels out stuff like MK's glide attack.
ftilt: if properly spaced, nothing, it is very safe on block, and has two hits
dtilt: pretty safe too.
utilt: on block, lots of things, this thing is unsafe on block lol
dash attack: sooooooooo laggy if blocked lol, do whatever is suitable
Jab: I'd assume an aerial out of shield would be good.
aerials: fair is kinda safe on shield in this MU, although you can probably try utilt, dair is probably not going to be punish with usmash, two hits + good range + the speed it is probably better to try aerial oos, utilt if it's in range, or grab if that's fast enough, although you can probably mindgame him if he doesn't know the MU (not relevant to MU discussion, but good to keep in mind with a MU).
Bair is pretty punishable if he tries the fair -> bair, nair if spaced will be tough, uair can probably be outranged by dair, but I'm not sure of Lucas dair's speed.
fsmash if spaced properly is going to be a bugger to punish even for lucas, but chances are that lucario will mess up and not do it properly. If so, I think grab or dsmash if it is fast enough might be able to punish it.
Most of these if improperly spaced especially dtilt can be punished readily, but remember that lucario plays best at a specific zone, so chances are he'll play at that zone as much as he can.