What is the official dress code rule in Venice for the Churches? How much leg needs to be covered? Is a skirt slightly below the knee enough?
Below the knees and shoulders covered.
knees and shoulders covered. If your skirt is that long, you'll be fine.
And that is for BOTH male and female.
As Doug said, both the knees and shoulders must be covered. Bring a scarf or something if you are wearing a dress that doesn't cover your shoulders. And this applies for almost every church in Italy, whether it's Venice, Siena, Rome, etc. Note: sometimes my dress came down to right above my knee, and I didn't have a problem. I'd say the focus is more your shoulders and really short skirts or shorts. If your skirt is below the knee you will be fine!