See this from the Internal Revenue Internal Manual (I'll underline the pertinent part)
Use the chart below to determine what TIN to enter in the Primary Applicant's Tax Identification Number field when the certification applicant is a Nominee, a FASIT, a Single Member LLC, a DRE-LLP, a DRE-LP, a Minor Child, a Q-Sub or a Sole Proprietor:
A NomineeEnter the TIN of the individual or entity the Nominee represents.
A FASIT (financial asset securitization investment trust)/IRC § 860HEnter the TIN of the FASIT's Corporate Owner.
A DRE-LLC, DRE-LP , DRE-LLP, or DRE-LLLPEnter the TIN of the single member owner of the limited liability company, limited partnership, limited liability partnership, or limited liability limited partnership.
A Minor ChildEnter the TIN of the person who claimed the minor child on the tax return.
A Q-Sub (Qualified Subchapter S Subsidiary)Enter the TIN of the Subchapter S subsidiary's parent, Line 6 of Form 8802.
A Sole ProprietorEnter the TIN used to claim the income on the individual's tax return.