For whatever reason, some weapons train the two-handed skill while others qualify as e.g. polearms or staves, despite also being two-handed.
These are all the weapons fitting in the former group:
<AdomDBbot> Death's Blade, Grod, Vanquisher, adamantium two-handed sword, axe of the minotaur emperor, eternium two-handed sword, great axe, heavy club, heavy skull club, mithril two-handed sword, two-handed sword, two-handed sword of parrying