Dear moosky,
The dutch are not so informal to say how are you doing. They would say how are you, or how are you today.
Hoe bent u? Hoe bent u, vandaag?
A litteral translation of how are you doing today is:
Hoe doe u? However, they may look at you questioningly.
Toastmaster
Toastmaster and former military who presided at many formal events and weddings;