Depends on how long you have to look.
It starts to come after a time that you will recognize patterns and potential as much as precise move count mates. I mean, if I have 2 rooks against your king, I know you are done, but maybe its 6 moves, maybe its 8, I don't know or care too much. But that is a dull example ... over time you start seeing things in more complex positions, -- hey that looks like a bishop assisting queen mate, but for that knight in the way, but wait I can sacrifice my rook to clear it down to the pattern I know, ... all come with playing a lot of games and experience vs how good your memory /pattern recognition is. And here again, knowing it will be a win in a bit is as good as knowing whether its in 2, 4, or 19 moves. Though the farther out you go, the more an unanticipated defense will ruin your day!
Thanks for your answers.
mau——