Every derived table (AKA sub-query) must indeed have an alias. I.e. each query in brackets must be given an alias (AS whatever), which can the be used to refer to it in the rest of the outer query.

SELECT ID FROM (
    SELECT ID, msisdn FROM (
        SELECT * FROM TT2
    ) AS T
) AS T

In your case, of course, the entire query could be replaced with:

SELECT ID FROM TT2