Full Moon Position of Sun I am trying to figure out the position of sun with respect to moon on a full moon day.

Here's an image from certain wiki which I do not find convincing.
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If the sun rays point as shown in the image and the earth stands between the moon and sun on Full moon's day, I dont see any reason why the moon should be shining in its full glory.

Similarly when the moon is directly in between earth and sun, it should have maximum brightness but the image shows it as the new moon.

In fact, I cannot deduce how at all can moon receive light across the entire sphere at any given angle from the sun.

Putting it specifically, what would the position of sun w.r.t to earth and moon on a full moon day ?
The orbits are not all in exactly the same plane, that is why we do not have eclipses every month. With the orbits at a slight skew it is possible to have the geometry very near to that in your diagram without the Earth blocking the Sun.

Lunar eclipses, the Moon passing through the Earth's shadow which is what your post is about, do occur relatively frequently compared to Solar eclipses because the Earth is bigger than the Moon.

At New Moon the lit side of the Moon is facing away from the Earth and so we do not see it.

You will find a fairly good explanation, and a better diagram, of all this here