Measure to Identify Values in table when filtered

If you just need it for one measure, you could use something like

My Measure = CALCULATE(
    SUM( 'Table'[Value] ),
    TREATAS( VALUES( Counter party slicer[counter_party] ), Counterparty_tbl[counter_party] )
)

  replacing the SUM with whatever calculation you needed.

If you want to apply it to multiple measures you could use a calculation group and create a calculation item like

Calc Item = CALCULATE(
    SELECTEDMEASURE(),
    TREATAS( VALUES( Counter party slicer[counter_party] ), Counterparty_tbl[counter_party] )
)

and then apply that calc item as a filter on the visuals you want to impact.