To handle multiple schemas in one DBContext

You can do the job by using -Schema parameter multiple times in this way though :/

 -Schema "dbo" -Schema "user"

All you need to do to provide multiple values is to use the 'array syntax'.

-Schema "schema1","schema2","schema3"

In your case, you have to do

Scaffold-DbContext "Server=localhost; Database=TestServer; Trusted_Connection=True; 
MultipleActiveResultSets=true;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models
-UseDatabaseNames -Force -Context "DbContext" -Schema "dbo","user"