-Dumat was killed by several GW at the same time,the GW order does not know who has absorbed it's soul that's why there is no name of the GW that killed Dumat beside a small reference to the Sentinels wardens(those who killed it),but it was killed for sure.
-Zazikale was ultimately killed by Corin through the help of Neria.
-Toth should have been killed by Loris a Dwarven GW however I'm not sure about it anymore as the writers seem to have changed that a little bit in DAI,Loris isn't addressed anymore as the killer of Toth.
-Andhoral was slain by Gharael.
-Urthemiel depending on player choice is either destroyed by Loghain/Alistair/one of the possible HoF or in Flemith/Solas hands or maybe was released in the fade,i don't know.
The others three(I'm assuming they are three because they could as well be two) are somewhere in the deep roads(except for this 3rd mysterious old god who is most likely beneath the ocean).