Can Lithoform Engine Copy Planeswalker Abilities?

Lithoform Engine can copy any spell or ability on the stack, not just one with targets.

Can you copy Planeswalker abilities?

You may copy a planeswalker's ability. Doing so won't affect the planeswalker's loyalty because raising or lowering its loyalty is part of the cost of the ability, not part of its effect.

Are Planeswalker abilities activated abilities?

Planeswalker Abilities

Planeswalkers have activated abilities. You can activate one of these abilities whenever you could cast a sorcery, but only one of a planeswalker's abilities may be activated during each of your turns.