Is it permissible to work in a field harvesting corn, knowing that a portion of it may be used to feed pigs in the West, and is this considered assisting in sin, requiring inquiry about the company's customers?

The basic principle concerning corn is permissibility. Its production or work with it is not forbidden unless it is used for unlawful purposes, in which case working with it becomes prohibited due to aiding in sin. There is no harm in working with corn harvesting unless it is certain or highly probable that it will be used for unlawful purposes. There is no need to inquire about the company's customers; what a Muslim knows to be forbidden, he avoids, and what he does not know, he does not seek to uncover.