for example, start with a simply cylinder and turn on the polyframe, I want to select every other row of a cylinder(every odd row or even row), I played with lasso select a bit but it seems to behave quite randomly, how to make such a multi selection in ZBrush?
If it is a primitive cylinder, the masking subpalette will have options to mask off rows and columns using a desired step number. For a polymesh, you might have to use the lasso to click directly on an edge, which should select it's entire loop.