The next Pokemon Go Community Day will take place on June 8, 2019 and will feature the normal-type Pokemon Slakoth! The event will also feature three-hour lures and 1/4 egg hatch distance. The exclusive move is yet to be announced.
The event will take place from 3:00pm to 6:00pm based on your local time. You still have an extra hour to evolve Slakoth or Vigoroth into Slaking and get the exclusive move.
Hopefully the exclusive move will make Slaking more useful besides just for defending gyms. It has a good attack stat (290) but it suffers from not so good moves for offense. A good Charged move would be Body Slam. It has 3 bars (instead of the 1 and 2 bar moves Slaking has) and will benefit from STAB (Same Type Attack Bonus). Another option would be a Fast move like Pound instead of Yawn, which deals no damage.