On the post effect’s Render tab, ensure the Post Render option is enabled.
On the post effect’s Multi-Pass tab, enable the passes you want to include.
On CINEMA 4D’s Render Settings / Multi-Pass tab, click the Channels button and choose Post Effects from the menu that appears. Render to the Picture Viewer.
That’s the core of it, more detail in the Help – Sketch and Toon Post Effect: Multi-pass