In SkySafari Plus and Pro, you can measure the distance between objects. Start by selecting an object you want to measure the distance from. Then 'tap and hold' the selected object to bring up the selection menu. Tap the "Measure" icon (looks like a ruler) from the menu. Tap on the object you want to measure to, and a line between your selected object and the object you initially selected will appear. The angular distance in the sky between the objects is shown at the end of the line, as well as the physical distance between those objects in space (if known).
Tap anywhere away from the distance measurement line to dismiss it or select "Measure" again from the 'tap and hold' selection menu.