The popping effect (indicated by P) is achieved by pulling the string with the index or middle finger of your right hand and at the same time turning the wrist outwards and then releasing it.
As it snaps back on the finger board and frets. it produces a more attacking rhythmic sound than that produced by the thumb alone. If a "popped" note is to be played following a slapped note you should place (P) under the string about to be popped at the same time the thumb (T) hits the note to be slapped, e.g., the two actions should be done in one movement.
This example introduces the popping effect combined with thumb slapping.
This example uses the same concept as previously shown but combined with hammer-ons after T and P.