B737-700 First Officer reported climbing above an altitude restriction departing LAS; citing distractions from checklist and wake turbulence as contributing to the incident.

Narrative

Flight LAS to ZZZ departed Runway 26R on the JOHKR 3. ATC issued us a level off at 12;000 ft. then notified us of a possible altitude deviation at KRUGR. The aircraft was being flown in LNAV/VNAV on B Autopilot with FL190 in the altitude pre-select window. Upon issue of new clearance to level off at 12;000 ft.; I reselected 12;000 ft. in the altitude pre-select window and disconnected the autothrottles to reduce the climb rate as we were passing 11;800 ft. The aircraft climbed to 12;150 ft. before leveling off at 12;000 ft. where I re-engaged the autothrottles. At this time we were told to look for traffic at 14;000 ft. which we had visually behind us. We never had an RA or TA. ATC then notified us of a possible altitude deviation at KRUGR. At this point we were approximately 24 miles past KRUGR on the JOHKR 3. We had briefed the departure and verified all altitudes and airspeed restrictions on the departure. Once established in cruise; the Captain and I debriefed the event trying to troubleshoot a possible error. One conclusion we arrived at was as we were approaching SELLZ I had asked him to delete the N1 restriction and he interpreted this as delete the ALT restriction at SELLZ since we were below the 8;000 ft. restriction. We didn't confirm the next waypoint as we got distracted with Climb Checklist and I believe a little wake turbulence from preceding aircraft. One thing would be to standardize the callout for deleting N1 reduction. I should have delayed the call for the Climb Checklist until work load permitted.