I have Zyxel mifi WAH7706. How can I get access to the content of the SD-card from a iPad or IPhone?

The WAH7706 uses Samba (SMB/CIFS) To share folders/files from the SD-Card on your network. Unless you have a way to access Samba shares from the iPad or iPhone I am afraid it will not be possible. I do not have much experience with Apple products so I would recommend contacting Apple to ask them the question if there is any way to access Samba shares from iPad or iPhone.