Word for "item after next"

On a different forum someone offered "Postproximate" in response to a similar request. The word doesn't exist right now, but hey, you never know, it might catch on.

"Subsequent" means "to follow" and is commonly used in cases like your example:

"To discover how I coded this program please consult the subsequent slide."

Definition and origin from MW-O:

"following in time, order, or place"

• subsequent events
• a subsequent clause in the treaty

Origin of SUBSEQUENT

Middle English, from Anglo-French, from Latin subsequent-, subsequens, present participle of subsequi to follow close, from sub- near + sequi to follow — more at sub-, sue First Known Use: 15th century

How about "...the second slide following." Truthfully, not every meaning can be captured in a single word.

In computer science, I think next next is somewhat common, but I don't think it's really used in other applications. However, that might be the most succinct term. Using it for your example, you'd get:

To discover how I coded this program please consult the next-next slide.

Other sites seem to uniformly use the form X after the next. For example:

To discover how I coded this program please consult the slide after the next.

I know this isn't a single word, but seems to be the most accepted usage.

Once again, not a single word, but baseball fans refer to the next batter as "on deck" and the following batter as "in the hole."

I would use "refer" rather than "consult", but either is okay.

To discover how I coded this program please refer to the 2nd slide over.

To discover how I coded this program please refer to the slide after next.