How to configure trunk on Cisco Catalyst Switch

Hi Rene,
I am, using WS-C2960S-24PD-L switch.
I got % Unrecognized command error message when I was going to config a trunk at interface Gi1/0/14.

CW2960#config terminal
Enter configuration commands, one per line.  End with CNTL/Z.
CW2960(config)#interface gi1/0/14
CW2960(config-if)#switchport trunk encapsulation ?
% Unrecognized command
CW2960(config-if)#switchport trunk encapsulation ▒

I would appreciate very much if you would explain the reason why?
Thank you.