Use the spell save DC.
The Draconic Presence does not present indeed any indication about the DC for the Wisdom saving throw. Anyway, we can read in the Spellcasting ability section:
Charisma is your spellcasting ability for your sorcerer spells, since the power of your magic relies on your ability to project your will into the world.
and moreover the description of Draconic Presence says (emphasis mine):
As an action, you can spend 5 sorcery points to draw on this power and exude an aura of awe or fear (your choice) to a distance of 60 feet. For 1 minute or until you lose your concentration (as if you were casting a concentration spell), [...]
Hence, since there is an explicit parallelism between Draconic Presence and casting a concentration spell, the DC for this feature is:
8 + Proficiency Bonus + CHA mod.
This is confirmed in some way also by the Frightful Presence feature of dragons: consider as an example an Adult White Dragon:
Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 14 Wisdom saving throw or become frightened for 1 minute.
The DC is 14, which is exactly 8 plus the proficiency bonus (+5) plus the CHA mod (+1). Another example is the Ancient Red Dragon:
Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 Wisdom saving throw or become frightened for 1 minute.
The DC is 21: 8 plus 7 (proficiency bonus) plus 6 (CHA mod).