Question

what is meant by 'I am sir Oracle' and 'let no dog bark '

Answer 1

sir oracle was very serious person.Here Gratiano is saying to Antonio that some people want to show wisdon so they maintain silent expressions on their faces. they want to become sir oracle.They want when they speak even dogs should stop barking.Gratiano compares Antonio to these kind of people.

Answer 2

Gratiano compares the behaviour of Antonio to that of Oracle or clergy in order to tell Antonio that his visage exhibits solitude and when he speaks let no oaf speak