can you react to orianna legend ability with energy conduit

Yes — you can respond to Orianna's legend ability, but Energy Conduit can't do anything to it.

Lady of Clockwork's ability ("At the start of your Main Phase, you may pay [1] to choose a friendly gear…") is a triggered ability, so it goes on the Chain and creates a Closed State where Reaction-speed plays are legal (FAQ #7676). Energy Conduit's ability is an Add ability — "[T]: [Reaction] — Add 1 energy" — so activating it while that trigger sits on the Chain just puts 1 energy in your pool; it doesn't counter, delay, or otherwise touch the legend ability (Rule 429.3). Its [Reaction] tag does let you activate it during that Closed State, and nobody can respond to the Conduit activation itself, since add-resource abilities can't be reacted to.

To actually affect Orianna's ability you'd need a Counter effect, and note the gear is chosen as the ability resolves — so killing a gear in response doesn't prevent the choice.