How to cut-slots in the middle of the PCB eagle?

[Gowda1]

I am wondering how to cut some shapes in the middle of the PCB. I am not sure on which layer I need to do and also no idea about how the manufacturers consider that? Please let me know on which layer I need to cut and also how to add it to CAM processor in order to see it has been cut. Is there any creepage distance I need to consider between the cut area and copper trace? I attach the picture for reference.

[Kean]

Normally I'd draw these in the milling layer (or maybe dimension layer).  Typically I'd just add a 2mm wide line, although I've done 1.6mm and 2.4mm.  Then check that the CAM processor includes that layer in one of the non-copper files (e.g. GML or GKO).  Look for them to appear in the preview during ordering, or ask sales support to check the slots.

You should check with the PCB manufacturer regarding minimum slot dimensions if you want thinner slots (extra charge).They'll also publish clearances from traces, but that is normally only critical for thin traces, not large pads for fills.  I'll sometimes have a slot between two pads 0.1" apart which may not meet published clearance specs, but doesn't cause any issues.

JLC PCB for example mention cut outs and plated/non-plated slots with Eagle on this page
https://support.jlcpcb.com/article/137-how-to-generate-gerber-and-drill-files-in-autodesk-eagle