What is the maximum speed of trunk/stack can be configured in WS-C3750G-24T-Switch?
No. As already mentioned above to have 10g interface, you gonna have to upgrade to 3750-E or 3750 or 3560 X series. They support 10GbE SFP+ Ports.
On 3750g, you proberbly can have max 8g by aggregating 8 ports in a port-channel.