In the Business Income (Sch C) section, where it says "Employer ID number", is it for the employer who issued the 1099 to the tax payer for whom i'm preparing Schedule C?

[Just-Lisa-Now-]

That would be for the EIN, if the business has one.

[George4Tacks · Accepted solution]

NO.
It is the EIN of the person for whom you are preparing the Schedule C. It can be left blank.

[IRonMaN]

As a side note, since you aren't sure about the EIN stuff, I'm guessing you haven't prepared a lot of schedule Cs.  In fairness to your client, your professional reputation and your professional liability insurance carrier, you really should consider doing a little homework about schedule C returns.  There are a lot of resources out there to help folks do things right so consider using them.