I haven't played in years, but in case you didn't read the walkthrough this is what I found:
Look and open the little oval panel and place the gem you in it that you got from the trunk. A light will be directed toward the big carved wooden desk. Go there and click on the look cursor in the center of the desk. The middle panel will open showing many pictures (the Brotherhood of the Dragon). Back out of that close up and look just below at the roll top part of the desk above the red blotter. Open that roll top panel and pick up the plaque, the medal of the dragon, the key and the cross in the circle. Now it is time to see Dorko!
Hopefully someone who has played more recently will come rescue you soon.