How to show only outline of an object?

I am a beginning at blue prints. I would like to show only the outline of an object. For example a circle. How do I only show only the outline of a circle instead of the full circle.

this could help Custom Depth and Custom Depth Stencil in UE4 - Superyateam Gamedev

First, you want it in 3d or on texture or in user interface. If in 3d then that custom depth material is best way. If that is in 2d read about materials and transparent textures (Alpha)