There are a variety of surgical approaches to this region of the forehead. To maximize your short and medium term cosmetic result, a hairline incision could be used. If you develop a receding frontal and temporal hairline later in life, this scar may be visible. A vertical scar in the glabellar region (directly over the osteoma) of the brow heals quite nicely and will be less visible as vertical lines of facial aging begin to appear.
First you would need to have x-rays to determine if the osteoma involves the frontal sinus. Assuming it doesn't an incision can be made either over it or at the hairline. It is better to make The incision with the Irregular Trico phytic forehead incision which we developed 35 years ago to get access to the osteoma and have a scar that does not show. See a surgeon experienced in this technique.