Q:

Can I cast the Wind Wall spell on an area I can't see? 

The description of the wind wall spell says:

A wall of strong wind rises from the ground at a point you choose within range.  You can make the wall up to 50 feet long, 15 feet high, and 1 foot thick.  You can shape the wall in any way you choose so long as it makes one continuous path along the ground.  The wall lasts for the duration. 

It doesn't say cast on a point that I can see like some spells say.  Does that mean I don't have to see the area that I'm casting it on? 

A:

Correct
You do not need to see the target area.  You still, however, need to have an unobstructed path to the target.  For example, you can't cast it on the other side of a wall or through a closed window. 
From the PHB:

A Clear Path to the Target
To target something, you must have a clear path to it, so it can't be behind    total cover. 
If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.