You can check them with a Gerber viewer, GC-Prevue is suggested for you.

ViewPlot is used by me for viewing my gerber files generated by Eagle. What I'm looking for mainly is the silkscreen, and that my drill holes line up with my solder mask.

1.Check inner layers for missing pads. 2.Check the notes. 3.Check that the layers are all present and numbered correctly. 4.Check for thermal relief, if desired. Check the stackup, including controlled impedance requirements. Are the pin 1 indicators visible, even when the parts are installed? Does the CM need panelization. If so, does it meet their requirements? Fiducials present for the pcb and BGAs (and panel) and they meet the CM's requirement. Make sure copper or silkscreen has the bare board part number and revision.

I will check if all layers are present and if all layers have data; If all layers are aligned and board outlines have the correct dimensions Make sure that soldermask is correct near high-density parts Making sure that Eagle merges the layers correctly.