Question:
Which two types of assignee(s) may conduct either the prosecution of a national application for patent or a reexamination proceeding?
Answer:
The assignee(s) who may conduct either the prosecution of a national application for patent or a reexamination proceeding are:

* (1) A single assignee. An assignee of the entire right, title and interest in the application or patent being reexamined who is of record, or
* (2) Partial assignee(s) together or with inventor(s). All partial assignees, or all partial assignees and inventors who have not assigned their right, title and interest in the application or patent being reexamined, who together own the entire right, title and interest in the application or patent being reexamined. A partial assignee is any assignee of record having less than the entire right, title and interest in the application or patent being reexamined.

Chapter Details:
The answer to this question can be found in chapter 400 of the MPEP. This chapter covers Representative of Applicant or Owner.
The answer is from the 9th Edition, Revision 07.2022, Published February 2023. Depending on future changes to the MPEP, the question and answer may or may not be applicable in later Editions or revisions.
Section Summary:
This question and answer comes from section 402.07 of the MPEP.  The following is a brief summary of section 402.07.
402.07 Assignee Revocation of Power of Attorney of Applicant and Appointment of New Power of Attorney
In applications filed on or after September 16, 2012, any power of attorney must be signed by the applicant or patent owner. In applications filed before September 16, 2012, the assignee of record of the entire interest can revoke the power of attorney of the applicant unless an “irrevocable” right to prosecute the application had been given as in some government owned applications.