I want to know what areas to cover for a case brief for International Trade and Investment Dispute Resolution specifically it deals with nullification and impairment (article 23)

I am a member of the complaining country under article XXIII of the GATT 1994. I need to write a brief complaining to the WTO panel that a benefit that acrued to my country  the EU under three rounds of negotiations has subsiquently been nullified or impaired by a measure enacted by the defendent country Japan. Japan is now offering subsidies to the local producers thereby nullifiying or imparing the benefits.