First suggestion: work under an Array modifier, based on a rotated Empty at the wheel's center. That way, all adjustments you make to one cog will be reflected in all the others.
But you could make a reasonably quick selection:
- Select one of the edges of interest
- ShiftG > select similar > direction
- In an orthographic view, using circle-select, enclose the unwanted (inner) edges in that direction, and middle-click, deselect those.
You can use Checker Deselect for this.
- Select all the edges around using Select > Edge Rings
- Deselect one of the edges (Shift + LMB) to break the loop
- Use Select > Checker Deselect (play with the values, and adjust offset if needed)
- Add that one edge to selection (again using Shift + LMB)