A Wild Magic Surge may happen when a Wild Magic sorcerer (PHB, p. 103-104) casts a sorcerer spell of 1st level or higher:
Once per turn, the DM can have you roll a d20 immediately after you cast a sorcerer spell of 1st level or higher. If you roll a 1, roll on the Wild Magic Surge table to create a magical effect.
Some magic items let you cast spells that are on the sorcerer spell list. For example, the Staff of the Magi lets you cast enlarge/reduce, which is a sorcerer spell.
Would casting a spell on the sorcerer spell list from a magic item have the potential of causing a Wild Magic Surge (for a Wild Magic sorcerer) ?
Best Answer
It would appear that this is possible.
The rules do support this outright. Per PHB p102 (emphasis mine):
And from DMG p141 under "Spells" (emphasis mine):
So if the item allows a sorcerer to cast a spell and that spell is on the sorcerer's list then your class feature would apply based on the wording. Also, see this answer.
It seems as though rules designer Jeremy Crawford says this is the intent in this tweet from May 2016 note that JC's Tweets are no longer official rulings.:
Keep in mind that a DM is free to ignore this as with anything else. Example: I could easily see a DM stating that your sorcerer's list is the one he knows not to include ones in the PHB under sorcerer that he does not.