TW3740 antenna for ublox M8T?

Hello, is suitable the TW3740 antenna for ublox M8T?, the gain is 40db for the antenna, that is the maximun for the Ublox receiver

Yes, it is perfectly suitable.

Is it possible to use an external antenna like this with the Drotek “Ublox NEO-M8T GPS + HMC5983 compass (XL)” board? I see that this M8T board appears to include a patch antenna, but I am unclear if it includes a connector for an external antenna. Thanks!

No, it has no external connector for this kind of antenna. In addition the design is different depending on if you are using an active or passive antenna (patch).