This is on South Gateway Rock - West Face. The Practice Slab is on the northern end of the West Face, and is easily spotted from the sidewalk. Once you've spotted the slab, walk to the south for about 25 feet until a trail takes you to the access ramp to the slab. There are chopped steps in the sandstone here that will take you to the anchors. Climb the steps, then traverse north across a ledge to the anchors.
The Practice Slab gets harder the more you veer north (climber's left). Choose your line. Belay from a large ledge at the bottom of the slab. The slab is one pitch.
Note: The anchors at the top of the slab get a lot of wear. I always back up the anchors with some of my own pro.
As I said above, backing up the anchors here might be a good idea. Bring a sling and some pro. One rope rap to the bottom here.