Díky za radu. Najednou mi to začalo fungovat.

javax.swing.JPanel jPanel1;
javax.swing.JLabel jLabel1;
jPanel1 = new javax.swing.JPanel();
jLabel1 = new javax.swing.JLabel();
jPanel1.setLayout(null);
jLabel1.setText("jLabel1");
        jLabel1.addMouseListener(new java.awt.event.MouseAdapter() {
            @Override
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                vvv((JPanel)((JLabel) evt.getSource()).getParent());
            }
        });
        jPanel1.add(jLabel1);
        jLabel1.setBounds(100, 100, 41, 16);
        jPanel1.addMouseListener(new java.awt.event.MouseAdapter() {
            @Override
            public void mouseClicked(java.awt.event.MouseEvent e) {
                vvv((JPanel) e.getSource());
            }

        });
        getContentPane().add(jPanel1);
        jPanel1.setBounds(230, 160, 260, 210);
        setBounds(100, 100, 400, 400);
    }

    private static void vvv(javax.swing.JPanel panel) {
        System.out.println(panel.getWidth());
    }