As we are moving in December within Spain
is my question, friend has a trailer(german plate) and said
we can use it for the move,
are we ok to hook it up to our spanish car.

what paperwork will we need or
is it easier to ask him to drive down with us

Depends on the size.
The law in Spain says -
Trailers with a maximum permissible carrying weight of 750 kg. It is advisable to incorporate the inertia brake. These trailers need not be registered, or be ITV.
Above 750kg
Trailers with a maximum permissible carrying weight of 3,500 kg. Have to have brakes. These trailers must be registered and have regular ITV.
You will have to have a number plate the same as your car.
To purchase this you have to show your registration documents. This is have your tow bar details on it. However when it comes to ownership. If it is the larger size I don't know how you can prove it. Maybe get a n export plate for it in Germany and ask your insurance company how you are covered.

Itv it has tüff as it is regiestered in germany.
he wants to lend it to us for the move only
I was just wondering if it is ok, do we need to take his trailer paperwork with us
like his proof of ownership??
Mind it is just like hiring it without paying

I have got no idea what documents would be acceptable to any Police force. It is not only Spain you have to think about. Maybe ask your insurance if you are covered for another persons trailer. Maybe they would know what is acceptable too.

now why on earth did we not think of that Thank you will ring them monday