AE to print material workflow

What ShiveringCactus suggesed as the way to export stillswould work fine or File > Export> Copy Fram to Clipboard (if you have a newer version of AE) adn paste into a photoshop file.

With 8K source footage  you will get @ 300 ppi an image that is:

Width: 25.6 inches

Height: 14.4 inches

It's a standard RGB to CMYK workflow (or whatever separations you need) like e.g. converting 3D rendered stuff. All that is required is to generate the pertinent metadata by opening it in Photoshop, changing the DPI to the required spec and adjusting the colors based on your color management. Outside that there is realyl nothing that would affect the AE side of things. If at all you may want to have an adjustment layer with e.g. a Levels or Curves effect somewhere to preview the gamut reduction, but otherwise there's really not much to it. A consistent CM workflow in PS is much more important than how you crank out your files in AE.

Mylenium

AE is pixel based, as opposed to dots per inch, but as Mylenium says, once you get the frame into photoshop, it should all be fine.  From your comp, select the frame you wish to use, then go to Composition > Save Frame As > Photoshop document or Save Frame As > File, which produces a single layer image.  You could also try Video Copilot's FX Console, which captures the frame to a temporary PNG file.  This works quite well, being based off the preview (I think).

Photoshop's upscaling is excellent these days, I recently saved a bunch of images out for an online merchandise store and on resizing in Photoshop they came out great.  Depending on your print medium, you'll likely also need to alter the colour space from RGB to CYMK, which can change the colours somewhat.

There is no standard workflow for such stuff, but of course nothing stops you from just rendering the frame and converting it to press-ready in Photoshop. Not sure what else you need to know here.

Mylenium