How Q11 works when Base is 0v?
You are correct that the base of Q11 is at 0V. However the circuit is likely to use an AC or transient signal that exceeds 0.7V periodically and that will turn on Q11. You'd need more detail as to the purpose of the circuit or the rest of the schematic to understand this.
Note that the base of Q11 is clamped by the diode on it's base and cannot go below -0.7V.