There is no UniGrid available in an MVC application. The UniGrid is an ASP.NET Web Forms technology, not an MVC one.
How to retrieve that data entirely depends on where that data is stored in the database for that Page.
If you are using a UniSelector as a Form Control for a Page Type field, then you are responsible for persisting the data stored in the UniSelector to the database.
Any additional functionality, such as database changes, must be implemented in the handlers of the control's events or using the Click event of a Button control used for confirmation.
If you have that part of this resolved, then you'll still need to query the database to retrieve the values that the UniSelector stored and this could be accomplished through several of Xperience's data access APIs.