What exchanges are supporting SegWit2x?
Most of the big exchanges are expected to support B2X, however there are a few that have announced they either aren't or are waiting until it's safe. Most of the exchanges that will support it, including Coinbase have also announced they won't be trading for 24 hours before the fork for security.

For now, these are the exchanges that have confirmed they will be supporting B2X:

Bitfinex
BitOasis
Bitrefill
Bitso
Bittrex
BTCC
CEX.io
Coinbase
Coinfloor
CoinNest
HitBTC
Luno
OKCoin
OKEx
Unocoin (However, delayed for up to four weeks)
ViaBTC
Xapo