May be it's just an easy question and I am being stupid or it's not possible..

Can you explicitly call trigger? meaning exec <trigger name>

You can't call a trigger. A trigger is a stored procedure that is executed when certain conditions are met. E.g. if you have an insert-trigger in a table, the trigger is only fired if an insert is done on that table.

B.t.w. this is also thouroughly explained in the Sybase-documentation.