Place 1 cup eggnog in a medium saucepan; sprinkle with gelatin. Let stand 1 minute. Cook over low heat, stirring gently, until gelatin completely dissolves. Stir in remaining eggnog, 2 tablespoons brandy, and vanilla. Remove from heat. Chill until consistency of unbeaten egg white (about 15 minutes). Fold in 1 cup whipped topping; chill until mixture is softly set. Cut pound cake into cubes; set aside.
To layer dessert in a trifle bowl, arrange enough strawberry slices, cut sides out, to go around lower edge of a 4-quart trifle bowl. Place half of pound cake cubes in bowl; sprinkle with 1 tablespoon brandy.
Combine remaining strawberries and preserves. Spoon half of strawberry mixture over pound cake; top with half of eggnog mixture. Top with remaining pound cake, and sprinkle with remaining 1 tablespoon brandy. Spoon remaining strawberry mixture over pound cake; then spoon remaining eggnog mixture over strawberries.
Spread remaining 2 cups whipped topping over trifle. Cover and chill at least 1 hour. Garnish, if desired.
Variation: To serve this trifle in wine glasses, layer ingredients as directed for trifle bowl, dividing them evenly to fill the glasses. Or prepare in trifle bowl as directed, and just spoon mixture into wine glasses (this method won't be quite as neat).
Note: Two 16- ounce packages of frozen whole strawberries can be substituted for 5 cups fresh strawberries. Just place whole strawberries in bottom of bowl. (If you slice them, they become mushy.