Skull

There are no sex differences for skulls until puberty.

After puberty the most obvious difference is the size of the skull. In Males the skull is larger and heavier than that in Females. 

The bony mass or thickness of the bone is thinner in Females.

The forehead in Males is slightly sloping or receding, whereas Females have a vertical flat forehead.

Face 

Typical markers of male & female faces:

The shape of the mandible is one of the differences between Male and Female skulls.
The more testosterone a man has, the stronger his brow, cheekbones and jaw line.
Males have larger more angular jaws. Females shorter more rounded jaws.

Example of a male and female jaw and chin

The overall lenght of the skull is longer, the chin is bigger and protudes more forwards in Males.
The superciliary arches are more marked in Males.
Males have a larger mouth and a larger dental arch.

In Females the facial bones are smoother, with smaller jaw and chin. Cheekbones are lower and less prominent.
The more estrogene a woman has, the wider her face, fuller her lips and the higher her eyebrows.
Females have a small mouth and a small dental arch.

Sex hormones control the divergence of male and female facial features.

Example of a male and female dental arch: 

Neck

Males have larger, thicker necks, due to their larger, heavier skulls. Their neck can be as thick as the width of their skull.
Their trachea is up to 40% larger. That protusion is called Adam's apple.

Females have shorter, thinner necks with commonly concave sides.

Example of a male and female neck

Typical female and male face

Not all of us have the perfect typical female or male face, but nonetheless there are lots of common markers. 

Training: Differences of faces - click here

Chin & Jaw Implants, Adam's Apple implants, Bone shaving, Face lifting and Hormone Therapy change the appearance of a face.

But does not change the size of the skull !

Watch Sex Differences in the skull: medical animation
https://www.youtube.com/watch?v=o3GvTnCuOIY

Feminization Surgery Transformation

A few examples of what is possible.

Masculinization Surgery Transformation

Training: Differences of faces - click here