The One Of workshop is a workshop for makeables located in Tinkertown.
For those who are under level 6, the One Of shop is just an empty shop. This shop gets its name because it so far only has one use, and one makeable. The makeable that can be made is the Tinkanoe, and a blueprint is needed.
The blueprint is located in Canopia Cove, on your first entry. It is part of The Rock Quest.