Several questions, and I think each one is a little different.
1. Ser Jaime Lannister (Valyrian) : "At the beginning of each phase, stand Ser Jaime Lannister."
... would this mean that Jaime stands up at the beginning of the Dominance phase, and his strength is counted to determine the winner of Dominance?
Is that a "passive" effect, or a triggered effect, or something else?
2. Court Archivist (Valyrian): "Dominance: kneel Court Archivist to draw a card."
... if I remember right, player actions come after you determine the winner of Dominance. So you would count the Archivist's strength to determine the winner of Dominance. And you can still kneel him afterwards to get a card.
3. Firemage and Eviscerate (Valyrian) ... almost the same kind of effect:
"Dominance: kneel Firemage and kneel 1 influence to choose a character without attachments. Until the end of the phase, that character gets -1 STR and is killed if its STR is 0."
"Dominance: kneel 1 influence to choose a character without attachments. Until the end of the phase, that character gets -2 STR and is killed if its STR is 0."
3a. Again, since player actions come after determining the winner of Dominance, Firemage's STR is counted for Dominance?
3b. Again, since player actions come after determining the winner of Dominance, the target of the effects don't suffer a STR penalty when the str for Dominance is being tallied.