Reasoning
Warcraft Tavern's Shaman guide recommends Leatherworking because Shamans wear leather then mail from level 40, and Forever's itemization philosophy favors spell-power gear that matters for caster Shaman specs. Engineering is the paired profession specifically because, per that guide, it now includes craftable Totems made for Shamans, on top of Engineering's usual gadgets and trinkets; the guide explicitly frames Engineering rather than Enchanting as the Shaman-totem profession. This conflicts with Warcraft Tavern's own Enchanting guide, which lists Totems among the relic types Enchanting can craft (with a named example, 'Mystic Mushroom,' as a Shaman Totem) — see conflicts. Source picks: Warcraft Tavern Shaman guide: Leatherworking + Engineering (Shaman-specific totems via Engineering); Koroboost (unverified): Skinning + Leatherworking OR Herbalism + Alchemy.
Confidence note
Analysis built from sourced profession facts