Which keyboard do they mean on organ when music says positif and recitive?
The answer depends whether you are asking about the physical arrangement of the manuals, or their musical function.
The "standard" 19th century French arrangement for a 3 manual console was Grand Orgue at the bottom, Positif in the middle, and Récit at the top. For instruments with more than 3 manuals, the additional ones were above the Récit.
On the other hand, in their musical function the Positif is closer to the English Choir and the Récit to the English Swell - i.e. a "standard" English 3 manual console has the "Positif" above the "Récit".
That's the theory, but in practice you may have to find the registrations that give the nearest equivalent registrations to the "French organ sound", and play them on whatever manual is most convenient. A typical small English Choir division is a very wimpy replacement for a French Positif with some "in your face" reed stops, and you might be better off using a reduced registration on the English Great, or coupling some stops from the Solo division of a large English instrument.
As a famous organist once said, "you never actually play 'composer X' or 'composer Y' on an organ. You always finish up playing 'composer X or Y, in an arrangement made by the organ-builder"!
(And as somebody else once said, "The only registrations you need to play any French organ toccata are a really loud noise on the manuals, a really really really loud noise on the pedals, and full swell with the box completely closed for the boring middle section that nobody listens to anyway.")