What was the turning point of d-day?

I'm not sure of you mean the actual turning point of D-Day itself, or how it was a turning point for the war, so I will briefly answer both.

Turning point on D-Day:

All things considered, there really were no major turning points during the day, as the entire invasion was a success. The Initial invasion by the allied paratroopers allowed key roads and bridges to be captured, and also allowed German artillery positions to be attacked (featured in Band of Brothers, at Breacourt Manor). On the beaches, the invasion forces were able to move inland relatively quickly, so there were points where D-Day looked as if it would be a failure, meaning there was no real turning point.

Turning point for the entire war:

D-Day was the most important turning point during the war due to its importance in stretching the German Forces and hitting the Germans hard. The combined effort by all of the allied forces on D-Day marked the turning point in the war, as it was the largest invasion attempt by the allies. It was also the start of US Operations in Northern France, and the US proved to be critical in defeating the Germans in Europe. On D-Day, around 156,000 Allied troops took part in the operation, around 73,000 of them American. With the massive assault on Europe, the Germans were forced to bring in troops from Russia and North Africa, stretching the German lines thin. This allowed the Russians to make major advancements, and the combined force of the allies and Russians led to Germany's defeat.