SketchUp can export its own drawings to several 2D graphics image formats including the PNG format. You can access the function with the File ► Export function. However you should know that this feature will only export one view of the 3D model, so when you would import this file back to SketchUp you wouldn't get the original model back. If you want to convert whole mode, use one of the 3D formats instead.
Convert SketchUp graphics to Portable Network Graphic.
We have found 4 software records in our database eligible for .skp to .png file format conversion.
Microsoft Windows software - convert skp to png on Windows
A widely-used 3D animation application from Autodesk
Convert from skp file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned skp to png. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A 3D general-purpose modeling program
A 3D CAD translation softwate
Apple macOS / Mac OS X software - convert skp to png on OS X
3D modeling application for Mac