The correct way to secure a block wall to existing concrete is to drill holes with a rotor hammer and concrete bit (1/6" smaller than your rebar) fill the holes 1/2 way with the proper epoxy and place the rebar into the holes. The epoxy will harden and secure the rebar. 

Build the wall with the rebar in the correct block cells, the top course of block should be built with lentil blocks (block with a U shaped top.) Once the lentil block is laid rebar should be placed in the U of the block and tied to the rebar coming out of the concrete and the entire top row of block filled with concrete forming a bond beam. 

Local codes are very strict about this process so be sure to check them for the proper depth of the holes, size of rebar, type of epoxy, and layout. Another thing you may want check is the footing requirements for the block wall, if the concrete slab was never meant to support the proposed wall you may face structural issues down the line.<o:p></o:p>