In SkySafari Plus and Pro, you can measure the distance between objects. Start by selecting an object you want to measure the distance from and then select "Measure From" by tapping the Selection button in the Toolbar. 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 "Cancel Measure From" from the Selection button in the Toolbar.