When do the Sun's rays strike the Tropic of Capricorn (23.5oS) most directly?

Answer 1

At that moment and at that location somewhere along the Tropic of Capricorn, it is solar noon. It also happens to be the moment of the summer solstice in the Southern Hemisphere, and the winter solstice in the north.

Answer 2

Winter solstice ... in the Northern Hemisphere.

Approx December 21. Beginning of Winter in the northern hemisphere, beginning of summer in the southern hemisphere.