Does anyone know of anywhere in NFPA 70E that requires a safety watch for testing and troubleshooting in a 480v cabinet?

There is not one. However OSHA has a requirement for CPR/1st aid.

1920.269(b)(1) "Cardiopulmonary resuscitation and first aid training." When employees are
performing work on or associated with exposed lines or equipment energized at 50
volts or more, persons trained in first aid including cardiopulmonary resuscitation
(CPR) shall be available as follows:

(b)(1)(i) For field work involving two or more employees at a work location, at least two
trained persons shall be available. However, only one trained person need be
available if all new employees are trained in first aid, including CPR, within 3
months of their hiring dates.

(b)(1)(ii) For fixed work locations such as generating stations, the number of trained
persons available shall be sufficient to ensure that each employee exposed to
electric shock can be reached within 4 minutes by a trained person. However,
where the existing number of employees is insufficient to meet this requirement
(at a remote substation, for example), all employees at the work location shall be
trained.

I hope this helps. OSHA does have a standard for using safety watch as indicated below.

1910.335(b)(3)

Attendants. If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees.

This is located under alerting techniques, NFPA 70E
Attendants, to warn and protect employees 130.7(E)(3)

No directive states specifically to watch the qualified worker. Attendants are only necessary when barricades are other methods will not keep non-qualified personnel away from the boundary area.

Industry specified documents, that I have created work practices for, include specific areas in which a qualified worker is not to work alone, e.g., roofs, plant exterior. (Normally, in isolated places were people could not observe an accident and come to the aid.)

As Zog says, OSHA has that pretty well covered. NFPA 70E also has a requirement for CPR training & first aid. But NFPA 70E does not imply that an attendant is used for anything other then, alerting of the hazard.

There are some companies who have emergency response personnel within 2-3 minutes response time that may exclude the need for qualified first aid training for workers, but in very little instances.

Longer response times may prevent onsite emergency crews reaching a subject quick enough. Then electrical workers may be required to learn CPR.