How do I skip validation for node form element?
I consider that by 


  How do I skip validation 


you mean "make the fields not compulsory" (UI level)

If that is the case then you can use hook_form_alter and change the 
['#required']
setting, for any form element, to 
FALSE.

Keep in mind that hook_form_alter is a generic hook invoked by any form in your site (performance issue) alternative you may use hook_form_FORM_ID_alter to "to talk" to a specific form. Hope that helps.

If you want to make the validation on a different level, you have to write your own validation handlers (['#validate']) or override Drupal's, like node_form_validate