For the Scene Layer Manager, there is a selectedlayer attribute.

For the Schematic view, there are two view attributes: AnchorPointID and Target.
Target is available for the node context menu only.

Here’s some code from the new Schematic example in the XSI SDK workgroup:

def XSILoadPlugin( in_reg ):
	#...
	in_reg.RegisterMenu(C.siMenuSchematicNodeContextID,"LogNodeInfo_Menu",False,False)	
	#...

def LogNodeInfo_Menu_Init( in_ctxt ):
	oMenu = in_ctxt.Source
	oMenu.AddCallbackItem("Log Node Info","log_info_cb")	
	return True

def log_info_cb( ctxt ):

	Application.LogMessage("log_info_cb called")

	# Returns the view object or a list with the view object and the target node (siMenuSchematicNodeContextID only)		
	target = ctxt.GetAttribute('Target')
	anchorPtID = ctxt.GetAttribute('AnchorPointID')
	# ...