which's

Of which; alternative to inanimate sense of “whose”.

Do you happen to know if - gosh, I've forgotten his name - from the zoo film unit is still operating at that little film studio which's name I've also forgot?

Of or pertaining to [some noun phrase ending with] which.

Whereas we are informed that the small pox prevails at New York, Connecticut, &c, the preventing of which’s coming into this place is of the utmost consequence, all persons are hereby notified that orders are given by us for all vessells coming into this port to hoist a jack at the main topmast head, […]

The yield is comparable to the best corporate securities, each of which’s principal is relatively safe.

contraction of which is

I didn’t ask for installation but they still charge me the installation which’s fine for me.

“Which’s the best man?” continued the young lady with the dark blue eyes.