Complex sentence: The Tleilaxu present Paul with a ghola in the likeness of his friend Duncan Idaho, killed during the events of "Dune", but secretly conditioned to assassinate Paul when triggered by certain words.
Split into simpler sentences: The Tleilaxu present Paul with a gift: a ghola in the likeness of his friend Duncan Idaho, who had been killed during the events of "Dune". However, they have secretly conditioned the ghola to assassinate Paul when triggered by certain words.