Dawn Phenomenon occurs because we are more insulin resistant in the early morning when growth hormones and cortisol are circulating.

Snogyi's effect occurs when blood sugar drops too low during the night and the liver counterreacts by producing glucose.

The only way to know which one you have is to test during the night, or use a continuous glucose montior.

If you're not on insulin, it's probably not Snogyi's effect. If you are on insulin, try going down on your nighttime dose. If blood sugar goes down, than it was Snogyi's. If blood sugar goes up, it's probably Dawn Phenom and you need more insulin.