Hi!
1. to kick - šutnuti, udariti nogom, ritnuti
to kick one's leg - šutnuti nekog u nogu, šutnuti nečiju nogu
2. napustiti (kuću/dom), otići, izaći iz kuće
3. What do you say? - Šta kažeš (na to)? (like "What do you think?")
What do you say (...when someone gives you a piece of candy)? - Šta se kaže (...kada ti neko da čokoladicu)?
Answer: Kaže se hvala. (for example)
"Šta se rekni?" could be only "Šta ste rekli?" - "What did you say?" (or What have you said?)
There is also "Šta se rekne...?" but that's....hm.. informal in our language. I think in Czech, for example, would be ok.