Turnover Percentage is an estimate of how many times a player turns the ball over per 100 plays they're involved in. It measures ball security relative to how often a player actually has the ball in a position to score or pass it away.
There isn't a clean position-based benchmark for TOV% the way there is for AST%, REB%, STL%, or BLK%, since turnover rate tracks usage far more than it tracks position. As a rough guide, a TOV% in the low-to-mid teens is normal for a high-usage playmaker, while anything comfortably under that for a similar role is a good sign of ball security.
Not necessarily. A player can also just be playing insanely safe and not doing much of anything that would generate a turnover in the first place, like avoiding tight passing windows or off-hand drives entirely.
There are a lot of different ways to cause a turnover, from live-ball reads to post entries to simple ball-handling mistakes, and those risks show up differently depending on a player's role rather than their position. A ball-dominant guard and a high-usage post player can both run hot for completely different reasons, which is mostly a function of usage, not position.