Is there a possibility of an English test waiver for New Zealand visa if I work with US clients in IT domain?

No, working with US clients in the IT domain does not typically qualify you for an English language test waiver for a New Zealand student visa.

English test waivers are usually granted if you are from an English-speaking country, have completed previous education in English, or hold qualifications taught in English. Professional experience, even with international clients, is not generally accepted as grounds for exemption.

For any possible exceptions, check directly with your chosen New Zealand institution, as requirements may vary by course and university.