Question about FX orders on session holidays

I was wondering when London has closed for the day and the USA has a holiday like today who looks after the FX BOOK as NZ and aussie markets are not yet open any sugestions ?

Not sure what you mean by "FX book".

Using today (Thanksgiving Day) as an example, the bigger Banks will usually have "night desks" manned by (at least) a skeleton crew to manage open trades, client orders, FX options hedging etc etc.

The markets are never really closed during a holiday like this.

Just FYI -- Canadian banks are still exchanging currency during the "New York session" on American thanksgiving.