2 maps here showing how often lightning strikes different areas of Earth across two different time periods. The data in the first was collected between 1998 and 2003; the data in the second was collected between 2012 and 2014. For the most part, the data from the two periods seem pretty comparable, focusing on the warmer and wetter areas.
The place where lightning occurs most often is near the small village of Kifuka in the mountains of eastern Democratic Republic of the Congo where the elevation is around 3200'. This region receives an average of 158 lightning strikes per square kilometer per year.
Lastly, pardon the two different map projections and styles.