I think it means a plain stat-only Will roll (i.e. SD+SD, with no rank or other bonuses from the Resistance: Will skill). i.e. roll open-ended, add your SD stat bonus twice, 101+ = Success.
Seems a bit weird and unfair, and makes the Talent grossly over-priced at 25 DP for such a small chance of success, but that's what the rules-as-written seem to say.
Personally, I'd make it use the Will RR skill, not just SD+SD. If a character pays DP for a skill and for a talent, they should get the benefit of the price they paid. Not doing so seems contrary to the basic premise of how HARP works - you get better at something (including focusing your will) by spending DP on it.