Query1.Close;
Query1.SQL.Text:='SELECT dni FROM alumnos WHERE nombre LIKE '+quotedstr('%'+txtnombre.text+'%');
Query1.Open;
Query2.Close;
Query2.SQL.Text:='SELECT cuota FROM cuotas WHERE dni='+quotedstr(Query1.FieldByName('dni').AsString);
Query2.Open;
showmessage(Query2.FieldByName('Cuota').AsString);