The IRS requires that a Third Party Settlement Organization (TPSO) provide a 1099-K to a payee if, for the calendar year:
See Box 1a. Gross Payment Card/Third Party Network Transactions for more detail.
1099-K forms are aggregated and sent by taxpayer ID, for each taxpayer ID that meets the requirements outlined by IRS.
If you have multiple restaurant locations associated with the same taxpayer ID, you will receive one 1099-K that aggregates the amounts for all those restaurants.
If each restaurant location is associated with a different taxpayer ID, you will receive a separate 1099-K for each taxpayer ID Grubhub has on file that meets the requirements outlined by the IRS.