Is it permissible to feed sheep with the waste products of liquor pressing (the seeds and outer skin), knowing that it does not intoxicate the sheep?

If you are pressing grapes to extract the seeds and outer skin for the purpose of making intoxicants, then this is not permissible, as it constitutes cooperation in sin. The Prophet (peace and blessings be upon him) said: "Allah has cursed wine, its drinker, its server, its seller, its buyer, its presser, the one for whom it is pressed, its carrier, the one to whom it is carried, and the one who consumes its price." However, if you do not participate in the pressing and you take the seeds and skin after their owners discard them, then there is no harm in that.