command_line.exe connect -s [IP-CheckPoint-Gateway] -f "[certificate file]" -p [Password]

Example:
c:program filescheckpointendpoint connectcommand_line.exe connect -s 195.19.17.178 -f "f:certfile.p12" -p secret

It is very important that the argument for the Parameter -f (certificate file) is set in quotation marks!