You’ve imported a file (such as STEP or IGES file) but it has come in as a surface model rather than a solid. Because your needs don’t require the file be made a solid, you decide to use the file as is, rather than taking the time to repair it to get it to a solid. The problem is it won’t show up in the drawing view.
In the drawing, expand the view node in the browser and locate the model node, then right-click and choose “Include All Surfaces”.
If the surface is a work surface in a part, you'll right-click on the top level of the part node:
If it is a surface based part in an assembly, you'll right-click on the the part node in the assembly tree: