Taali is a clap in Hindi. Taali bajaana is the verb, which means 'to clap.' When you have to ask someone to clap, you say, taali bajaao, or taali bajaa, or taaliyaan bajaaiyay [the last one being in plural, respectful way].
However, Navjot Singh Siddhu, the man on Comedy Nights on Kapil and many comedy shows before that, has a different style of saying this thing. Instead of saying Bajao, he says 'thoko'. Thokna in Hindi means to strike, hit, most commonly to hammer, to drive something, like a nail, in with the hammer.
Another thing, instead of Taali Thoko, he says Thoko Taali. The order doesn't really change the meaning, but he just emphasizes the verb, the action more. That is the reason sometimes he just says thoko instead of complete 'thoko taali', too.