Does a commercial tenant need the new owner's consent to assign or sublease after a building sale?

This question actually involves two different kinds of assignment that are easy to mix up. When the building itself is sold to a new owner, that's an assignment of the landlord's interest. The tenant's consent isn't required for that, and the tenant's lease simply continues automatically with the new owner stepping into the landlord's role.

The consent requirement most leases impose is the opposite situation: if the tenant wants to assign its own lease or sublease its space to a different, new tenant, that typically does require the landlord's consent under most commercial lease clauses, usually with a standard that consent can't be unreasonably withheld. That consent requirement applies to the tenant's side of the relationship and continues to apply after a building sale, with the new owner simply becoming the landlord whose consent is now needed for a tenant-initiated assignment or sublease going forward.

So the short answer is that a tenant doesn't need to do anything, or get anyone's consent, just because the building was sold to a new owner. But if that same tenant later wants to bring in a different tenant through an assignment or sublease, the new owner's consent as landlord will generally still be required under the lease.