Indexes (arrays) work the same way in JASS (custom scripts) as in regular GUI: you wrap square brackets around them.
"Player number" in JASS is GetPlayerId( player )
, the difference is that in JASS Player(0) is red (Player 1 in GUI). So you have to add 1 to that number.
"Owner of unit" is GetOwningPlayer( unit )
"Killing Unit" is GetKillingUnit()
The finished result becomes: call RemoveLocation( udg_variableName[ GetPlayerId( GetOwningPlayer( GetKillingUnit() ) ) + 1 ] )
That is with spacing so it - hopefully - becomes a bit more clear.
Note that if there is no wait in your trigger (between setting the location and removing the location), you don't need an array for this at all.