After enabling Requisitions under Setup > Company > Setup Tasks > Enable Features > Transactions sub tab, purchase requisition is added as part of the transactions you can perform in your account.
However, the ability to perform Purchase Requisitions in bulk via CSV import is still an enhancement request.
See enhancement : 385050 - CSV Import: Ability to upload Purchase Requisitions for more information.
This is still not available as of November 17, 2019.