Answer
No — a user's currently-selected Company (as opposed to their default one) isn't stored at the database level at all; it's purely a client-side concept that only gets passed into a database API call as an explicit argument when the client makes that call, never persisted server-side for a database-level lookup to retrieve independently. The only company-related value retrievable directly from the database is the user's default company, via User_Finance_API.Get_Default_Company_Func — if your custom code needs to know the currently-selected company specifically (not just the default), that value has to be passed in explicitly from the client-side context that already has it, not looked up server-side.