What does Mr. Brownlow demand that Monks do for Oliver?

He wants him to sign an official document that provides confirmation of who Oliver is, and to make sure that everything Oliver was entitles to is provided for him;

'You must do more than that,' said Mr. Brownlow. 'Make restitution to an innocent and unoffending child, for such he is, although the offspring of a guilty and most miserable love. You have not forgotten the provisions of the will. Carry them into execution so far as your brother is concerned, and then go where you please. In this world you need meet no more.'

to give money to oliver and sign the papers