Creating and editing large graphs and node-link diagrams are crucial activities in many application areas. For them, we consider multi-touch and pen input on interactive surfaces as very promising. This fundamental work presents a user study investigating how people edit node-link diagrams on an interactive tabletop. The study covers a set of basic operations, such as creating, moving, and deleting diagram elements. Participants were asked to perform spontaneous gestures for 14 given tasks. They could interact in three different ways: using one hand, both hands, as well as pen and hand together. The subjects' activities were observed and recorded in various ways, analyzed and enriched with think-aloud data. As a result, we contribute a user-elicited collection of touch and pen gestures for editing node-link diagrams. The study provides valuable insight how people would interact on interactive surfaces for this as well as other tabletop domains.