Half the loft

As a general rule, you want to launch your distance wedges at about half the loft. I like to use an alignment stick to help create the visual of the trajectory. You can set up the alignment stick either by approximating half the loft by stepping on the club and getting the clubface parallel to the ground. Or you can use a 7-iron (approximately 30 degrees) or 6-iron (approximately 26 degrees) to help approximately that angle the ball should launch at.

Keep in mind that in order to get a low launch you need to play a premium ball, with a clean wedge, and make solid contact with some shaft lean in order to get in the ballpark of the right launch angle.