Q: Will there be KGB in communism?
A: As you know, under communism, the state will be abolished, together with its means of suppression. People will know how to self-arrest themselves.
The original version was about the Cheka. This joke refers to an early Soviet practice called samooblozhenie ("self-taxation"): in addition to the standard taxation to which the peasants were subjected, they were often forced to deliver a normal amount of agricultural products, while prosperous peasants, especially those declared to be kulaks were expected to "voluntarily" deliver the same amount again; sometimes even "double samooblozhenie" was applied.
Q: Is it true that there is freedom of speech in the Soviet Union, just like in the USA?
A: In principle, yes. In the USA, you can stand in front of the White House in Washington, DC, and yell, "Down with Reagan!", and you will not be punished. Equally, you can also stand in Red Square in Moscow and yell, "Down with Reagan!", and you will not be punished.