Should I power up this snorlax

depends on CP of other snorlax

42% is too low...i wouldnt power both cuz snorlax candies are rare and dust are precious. Wait for a nice IV with a nice moveset then you power up.

EQ isn't much worse than HB. Depending on the CP of the EQ one I'd look at powering that one up. The HB one will still make a decent attacker unleveled up.

Earthquake is rated at 23.81 defensive DPS while Hyper beam is 30 defensive DPS (with STAB) .. so you'd do more damage defensively with the lower IV poke. However .. your CP would be significantly lower, so that does impact your slot in gyms. You can't really go wrong with either though - they are both Snorlaxes! I'd raise them both.

Walk it to get candies. If you get enough candies to raise it to ~27 before you get a better Snorlax, then raise it (or the other one). If you get a better Snorlax, raise that one instead and keep walking to raise a second one after.

I have a 52% Zen Headbutt / Body Slam Snorlax and he's done amazing for me on defense, regardless of IV. He's also higher CP than all but my Dragonites even with just 52% IV. (even higher than my 82% Lapras).