How do you monitor specific SQL statement of a specific user ?
You might want to look into AUDIT ALL STATEMENTS BY user. As per Oracle's documentation, audit all statements by ...  audits all top-level SQL statements executed. Top-level SQL statements are issued directly by a user. SQL statements run from within a PL/SQL procedure or function are not considered top-level statements. Therefore, this clause does not audit the statements executed within PL/SQL procedures or functions. However, the execution of the PL/SQL procedure or function itself is audited. This clause is useful if you want to audit all the statements in a specific environment, regardless of other auditing configurations that are system wide or user specific.