Beat cream cheese, sugar, zest, and 1/2 tsp. vanilla at medium-high speed with a heavy-duty electric stand mixer 30 seconds or until smooth and sugar is dissolved. Fold in whipped topping, and spoon into a 1-gal. zip-top plastic bag. Seal bag, and chill 2 to 24 hours.
Peel clementines, and separate into segments. (Yield should be 4 cups.)
Microwave marmalade in a medium bowl at HIGH 20 seconds or until melted. Stir in clementine segments, poppy seeds, and remaining 1/2 tsp. vanilla. Remove and reserve 6 segments. Divide half of clementine mixture among 6 (10- to 13-oz.) glasses. Top each with 2 cookies. Repeat layers once.
Snip 1 corner of bag with cream cheese mixture with scissors to make a 1-inch hole. Pipe mixture onto cookies in glasses. Serve immediately, or cover and chill 2 hours. Top with reserved segments just before serving, and garnish, if desired.
Note: For testing purposes only, we used Anna's Ginger Thins. A 2 1/2- to 3-qt. trifle dish may be substituted for 6 (10- to 13-oz.) glasses.