How can I add a skip button above the webform (with multistep)
It seems that basically, you want a copy of "next", but with different title and placed on top. To achieve it:


Examine structure of form you are alerting. Find where original "next" is defined.
Create a copy of it. Use code like:

$form['my_skip_button'] = $form['path']['to']['next']['button'];


You Don't really need to know or care what it is, you need a copy, so you go and make a copy, simple as that.
Set weight to something low to get it to top:

$form['my_skip_button']['#weight'] = -10;

You can alter the title in the same way you altered weight.