Does deathtouch apply when a creature deals damage to a planeswalker?

Deathtouch is a static ability that states any amount of damage dealt by a source with deathtouch is sufficient to destroy a creature (CR 702.2b). The key word here is creature. When a creature with deathtouch deals combat damage to a planeswalker, that damage removes loyalty counters from the planeswalker, but deathtouch's destruction effect simply does not apply to planeswalkers.

CR 702.2c specifies that a creature with deathtouch that deals damage to another creature causes that creature to be destroyed. Planeswalkers are not creatures (unless a card specifically makes them so), so they fall entirely outside the scope of this rule.

Planeswalkers are instead governed by CR 306.7: combat damage dealt to a planeswalker causes that many loyalty counters to be removed. If the planeswalker reaches zero loyalty counters, it is put into its owner's graveyard as a state-based action (CR 704.5i) — but this has nothing to do with deathtouch.

Concrete example: Your 1/1 Snake with deathtouch attacks and your opponent redirects the damage to their planeswalker. The planeswalker loses 1 loyalty counter. It is not automatically destroyed by deathtouch; it only goes to the graveyard if that removal brings it to 0 loyalty counters via normal state-based actions.

In summary, deathtouch is irrelevant when the damaged permanent is a planeswalker. It only triggers destruction for damaged creatures.