If a player holding several cards is unable to follow suit but holds at least one trump card, is that person required to play one of his trump cards or can he/she continue to hold his/her trump cards and play another suit card.

I know it's not required by the rules but one of our players wants this questioned answered by knowledgeable players.

Player is not required to play trump. The only time you have to play trump is if it's suit led. Of course, Wizard or Jester may be played at that time..saving your trump for a more opportune time.