I use the following in the MouseDown event to detect the node:

LPARAMETERS pnButton, pnShift, pnX, pnY
LOCAL loNode
IF pnButton = 2
	loNode = this.HitTest(GKKPixelsToTwips(pnX,"H"),GKKPixelsToTwips(pnY,"V"))
	IF VARTYPE(loNode) = "O"
		this.RightClkMenu(loNode)
	ENDIF
ENDIF

This is used to call a right-click menu. I have a UDF to get the pixels to Twips.