I am looking at this card:

Dorne.

House Dyane characters get +1 STR for each gold token on them.

Respons e: After you in a challenge in which a House Dayne character participated, place 1 gold taken from the treasury on that character.

During taxation does that gold get removed? I think not because taxation say to return all gold from each players gold treasury. I do not think gold on a a character is the gold treasury.

Can this response be used more the once per phase? I think yes because it does not kneel when you use it.

It says to place the gold on "that" character? What happens when there is more the one House Dayne character? I assume each participating character would get a gold.

Can the gold be spent? I think not because I think the rules say the money can only be spent from the players gold treasury.

Thanks for the help!

Don

The gold does not get removed during Taxation, it works the same way as Core Tywin.
The Response can be used more than once per phase, but only once per challenge and you can only place a gold on a single Dayne character because of the way Responses from cards in play work; the controller of Starfall would choose which character to place the gold on.
You cannot spend the gold (again, see Core Tywin, the card specifically states that you can spend the gold as if it were in your gold pool) but you could use a Southron Vessel to move the gold.