On Jeopardy, are you blocked from ringing in until the question has been completely given or can you ring in as soon as you know the answer? Also, are you able to read the question while Alex recites it like the TV audience, or do you merely hear Alex recite it?

You are able to read the question like the TV audience. (The screen is on the other side of the studio so near-sighted players might want their eyeglasses.)

You are blocked from ringing in until the question ends and a studio engineer flips a switch. Supposedly, if you ring in too early, you are locked out for a half-second before you can ring in again.

A light goes on to tell you that the switch has been flipped, but if you wait to react to that then you will probably be too late. Instead, you need to anticipate the end of the question and try to get into the rhythm of Alex and the studio engineer.

This is the way that “Jeopardy” does it, and the way “Win Ben Stein's Money” did it.

Some alternative things that could be done are:

Let players ring in as soon as they know the answer, and stop reading the question when they ring in.  This is the way that “GE College Bowl” did it and the way “Winning Lines” did it and the way “University Challenge” does it.

From a quick-thinking player's perspective, this is probably the best and fairest way to use buzzers, since it rewards fast recall or fast reasoning, does not reward blind aggression, and makes the buzzer race more meaningful than a coin flip.

From a TV producer's perspective, there are downsides. The TV audience has less chance to answer the questions at home, and may be baffled when good players cut off the moderator after a couple of words. The time it will take the players to answer a given number of questions becomes more variable. There is an art to writing questions that can be interrupted halfway through. And if all is done correctly, then the better and faster player becomes more likely to win, which the TV producer may not consider an improvement if the TV producer craves unpredictable games.

Let players ring in whenever they like, but still finish the question for them or let them read the question. I've been told that Jeopardy tried this approach in their earliest episodes.

The problem was that players who were behind would start buzzing very aggressively, gambling that they would know the answer by the end of the question. If it didn't work, then they would become even more desperate-aggressive and tended to implode into negative scores, making the later stages of the game moot.