Complex sentence: The 35-page dossier claims that Russia is in possession of damaging or embarrassing information about Trump which could be used for purposes of blackmail to get Trump to cooperate with the Russian government, which includes allegations about Trump's sexual and financial dealings in Russia.
Split into simpler sentences: The 35-page dossier claims that Russia is in possession of damaging or embarrassing information about Trump which could be used for purposes of blackmail to get Trump to cooperate with the Russian government. The material includes allegations about Trump's sexual and financial dealings in Russia.