The leak comes from above where water comes out.
Turn off power before touching wet electrical appliance.
Put stopper in disposal.
Fill sink with water.
Check if water is getting through the putty seal at sink connection.
Next, check if water leaks only when dishwasher runs. Dishwasher drains into garbage disposal.
Last, check tailpiece where it attaches to side of garbage disposal. The tailpiece is usually sealed with a rubber washer. When washer is old, it gets deformed, and then it doesn't seal perfectly when put back.
I use rectorseal on all tubular pipe joints under the sink.
Works on both plastic and rubber washers.
It is gooey and sticky.
Brush it all over the washer, use plenty, then assemble pipes.
The rectorseal assures that joint will not leak.