To pull asset's 24-hour volume you can use the /volume slash command. Start a request by specifying a ticker ID in the ticker field. After an instrument is specified, you can also provide an exchange or venue in the venue field.
If you do not specify an asset class, it'll be picked automatically based on closest matching assets with a bias determined by server's ticker parsing preference. If you do not specify an exchange or venue, the default is determined automatically based on an internal exchange and venue priority order.