At what time of the year do regions at latitude 60'N degrees absorb the most solar energy /Why?

Answer 1

The first day of summer. That is the day the sun comes the highest overhead, as well as the longest day of the year.

Answer 2

The longest day of the year (with clear skies!). This is 21st June for northern hemisphere.

This is true for all non-tropical latitudes, not just 60 degrees. In the southern hemisphere it's 21st December.

There is maximum solar energy reaching the surface at that point on that day.