How do we know about the first comma in the Gandhiji's example
Let us understand one of the various usages of commas:
A comma is used after phrases of more than three words that begin a sentence. If the phrase has fewer than three words, the comma is optional.
For instance: To get admission here, you must have a lot of knowledge and common sense.
On February 14, many couples give each other candy or flowers.
This explains the comma in the given sentence:
In his autobiography, Gandhi makes it clear that he wished to tell the story of his “numerous experiments with truth.”
In his autobiography, Gandhi makes it clear that he wished to tell the story of his ‘numerous experiments with truth’.