SELECT *
FROM posudivanje AS p
INNER JOIN knjige AS k ON p.idKnjiga=k.id
INNER JOIN zaposlenici AS z ON p.idClan=z.id
WHERE p.datum='2020-06-02'
AND k.id=(SELECT p1.idKnjiga
          FROM posudivanje AS p1
         WHERE p1.idClan='1' AND p1.datum='2020-06-02')