I would like a simple check to highlight nets which connect only to gate(s) (n and/or p) and only ntype S/D diffusion.
I am not sure which way to address it
This is probably best done with an ERC check. Take a look at Example 3 under Device Layer in the SVRF Manual. See if that helps give you a start.
Highlighting whole nets may be a bit of a challenge and could potentially cause a lot of output. Perhaps limiting the output to just the nsd and gate polygons on a net may be desirable. Using Net Area Ratio with the RDB ... BY LAYER keyword with the two layers in question may be useful.
Retrieving data ...