Hi, 
If you have a O2M with a button in each line. When you click on that buton the record's form view should be displayed, then you only have to add this exemple: 

def open_one2many_line(self):
   self.ensure_one()
   return {
        'name': _('Something'),
        'view_type': 'form',
        'view_mode': 'form',
       'view_id': xml_id of your view, 
        'res_model': self._name,
        'context': self._context,
       'type': 'ir.actions.act_window',
       'nodestroy': True,
       'target': 'current',
       'res_id': self.id,

        }

You don't need a menu as the view types are linked to the action, not to menu.

Hopethis helps. upvote if it does.

Regards.