How to get the value of autoincrement of last row at the insert

Use SCOPE_IDENTITY:

-- do insert

SELECT SCOPE_IDENTITY();

Which will give you:

The last identity value inserted into an identity column in
the same scope. A scope is a module: a stored procedure, trigger,
function, or batch. Therefore, two statements are in the same scope if
they are in the same stored procedure, function, or batch.