Where do I place pressure ports on an airfoil?
Depends on what you want to measure.

Normally, pressure ports are bunched close to the leading edge to give sufficient resolution of the steep pressure gradients (which result from the high local curvature). So scale the local pressure port distance with local curvature.

But maybe you want to have a high resolution of the beginning flow separation near the trailing edge? Then you need to place the pressure ports close to the trailing edge.

Or maybe you want to study the laminar to turbulent boundary layer transition at mid-chord? Then any pressure ports in the laminar region will cause a local transition and show a 15° cone of turbulent flow which will mess up all other measurement behind them. Now you need to restrict the number of ports in the forward part of the airfoil and need to give them enough lateral separation to get what you want.