Given circuit is based parallel clipper. to determine output waveform $V_0$, Consider,

Case 1: (0 to T/2)

When $V_{in}$ > 4v, Diode will be forward biased & it will act as a closed switch. Also, the given Diode is of silicon type, therefore in forward biased condition voltage drop across Si diode will be 0.7. So, the equivalent circuit will be:

Now, for Vin < 4V < 0V , Diode will be reverse biased & equivalent circuit will be,

Case 2: (T/2 to T)

Here, as $V_{in}$ < 4V, Diode is reverse biased and acts as open switch

Therefore the equivalent circuit will be,

Now, the complete circuit output voltage for a given biased parallel clipper can be drawn as shown below :