How do I cut grooves in self-leveling concrete to incorporate an existing drain?
24 sq ft would be an area approximately 4x6?  Adding two inches of depth... I think what I would try in this case would be to get several 1/2" dowel rods and cut them to lengths that would allow me to align them in a radial pattern out from the drain, something like this:



Around the drain, I would prop them 1.5" up in the air, and at the periphery I'd prop them 2" up in the air, that way when I poured, I'd end up with 1/2" deep semi-circular troughs that ran downhill towards the drain.  Pour concrete, let it set up and remove the dowels.

DEFINITELY add a new drain cap on top of the old one as a 3" diameter 2" deep hole in the floor is a serious trip hazard.