In the Standard style of ballroom dances. Is there an exact position for the man's head, which is looking to the left, but how far.

over the lady's R shoulder.

A smart comment here would be "depends where the lady's right shoulder is". but more seriously, there isn't an exact specification as dancing is an art-form. If straight ahead is 12 o'clock, then 10.30 isn't a bad starting place. This is just for normal closed position of course.

Yes, there is a specific location where the man's head should be.

In Standing Position, it is approx. nose over your toes. When travelling, it will move between 3/16th and 1/16th anti-clockwise from normal straight-forward position (that's between 10 and 11 o'clock, per phil.samways's example. It will move because of CBM and other rotational actions.

Is it acceptable if lady's head in 10 o'clock in normal closed position ?

Sorry to be graphic, but I've heard it expressed as "nose over nipple"!

If you are any good at looking at as is with todays top dancers, you will find it is left cheek over left nipple. Straight ahead is useless. Cheek over left shoulder is to far, the neck will twist and also shorten. The head is not in a fixed position. There is balance and counter balance. A lot more is going on than that. The body in some moves does move under the head. but will come back to its original position.
Just my thoughts. Try a Whisk starting with the head in the correct position. It will appear that the head has turned left. It hasn't really, the body has moved not the head.

Your observation and thoughts here are reasonable . Thanks for sharing.

You are talking about smooth, of course, not rhythm or Argentine Tango.

Jerry