Before entering on a hold (stack), the ATC should instruct the turns and headings to be accomplished by the crew. If it is not printed on the charts, as on STARs, what is the correct phraseology to be used by ATC?
You didn't mention any particular country or jurisdiction, but for the US the FAA's ATC orders say in section 4-6-4:
HOLD (direction) OF (fix/waypoint) ON (specified radial, course, bearing, track, airway, azimuth(s), or route.)
If leg length is specified, (number of minutes/miles) MINUTE/MILE LEG.
If direction of turn is specified, LEFT/RIGHT TURNS.