You can use tpt.selectedl for this (there is also tpt.selectedr, tpt.selectedreplace, and tpt.selecteda).

tpt.selectedl returns something like "DEFAULT_PT_SPRK". You can do elem.DEFAULT_PT.SPRK or elem[tpt.selectedl] to get the ID from this.

You can also set tpt.selectedl to anything, like tpt.selectedl = "DEFAULT_PT_GRVT" or tpt.selectedl = elem.property(28, "Identifier")

@TPT_PL (View Post)
Yes, it has to be an identifier string. There are simple ways to convert between that and an ID that I showed in the post.