How to research a company which is going public before making an investing decision?

Any US company going public has to file with the U.S. Security and Exchange Commission. Those documents are public and accessible.

From the SEC page on IPOs:

How do I learn about the company?

A company undertaking an IPO discloses required information in the registration statement, typically on Form S-1. Form S-1 and its amendments, which are denoted as S-1/A, are filed with the SEC and publicly available through the SEC’s EDGAR database at Search EDGAR. Comment letters issued by the staff during the course of an IPO filing review are also made available on EDGAR, but they are not posted until at least 20 business days after the registration statement is declared effective.

Most of a Form S-1 is comprised of the prospectus, which contains important information about the company. A new public company typically has no prior reporting history, and the information that can inform a decision to invest often can only be found in the prospectus, although, if it has sold securities in reliance on an exemption, the company may have filed one or more notices on Form D.

That page has a number of resources and suggestions on how to analyze a IPO.

What about data/information/analysis not in the SEC filings?

Beyond what is filed at the SEC will depend on your research:

• Your individual industry knowledge
• Your individual interactions with the company
• Information any Wall Street financial analyst provides (free/paid)
• Trade publications
• Any news/press releases