someone know when is the 737NG "sink rate" warning be triggered?

[PEI_3721]

citizensun, see Operation - EGPWS - Honeywell Aerospace and download the appropriate pilots guide.
I don’t know the exact part number applicable to your aircraft; I suspect that it will be the ‘Mk V and Mk VII’ version.
Perhaps a 737 expert will provide information on the exact model.

My understanding is that mode 1 works at all altitudes; and don’t forget that the alert depends on Vertical Rate against Rad Alt.
Also don’t forget mode 3 after take off.