As Raj123 said, Indian court orders will not be valid in US or any other country.
You should be able to submit his India job and payslips and file a case of maintenance.
Let the maintenance petition be registered and summons served to the known address of your sister's husband.
Then, you can request court to order her husband come up with his salary details.
Let the legal process kick in so that the husband is brought into legal procedure.
You can try to record the conversation when you talk to his "female" friend and other fiends and use it as a proof that he is working.
On the other hand, It is highly unproductive for a wife to chase her husband's salary details.
If a wife cannot live with her husband, she should have a plan to support herself on her own efforts.
That signifies the dignity of a woman as the mother of a kid.
More than the payslip, the wife needs her husband.
More than she needs her husband, her kid needs her father. It is the birth right of the kid.
This forum hopes that parents live together at least for the sake of the child.
Because a wife can file a case of maintenance and get some money after a long fight.
But, she will never do any good to her kid by denying the kid, the right to live along with kid's father.