Prepare Jamun Puree:
In a blender, combine deseeded jamun, mint leaves, black salt, sugar, chaat masala, roasted cumin powder, jaljeera powder, lime juice, and ice cubes. Blend until smooth and frothy. Set aside.
Rim The Glasses:
Mix salt and red chili powder on a small plate. Rub a lime wedge around the rim of shot glasses. Dip the rim into the salt-chili mixture to coat evenly.
Assemble Fuljar Soda:
Pour the jamun puree into the prepared shot glasses. In a tall serving glass, add a few ice cubes and pour chilled club soda halfway or more, depending on your glass size. Carefully drop the filled shot glass into the soda-filled tall glass and watch it bubble up.
Serve Immediately:
Enjoy the fizzy eruption as the flavors mix. Drink immediately while it's still bubbly and cold.