Nexus is on PTS, but it is instanced much like the Tutorial. Currently the only way in is for it to be created by an admin and warped in. That is typically done for Community Clash on Wednesday nights.
Some players who were already in Nexus (like a participant on a previous CC) can log back into it, and if you want to check it out you might be able to have one of those players squad with you and quick deploy to them. However, we cannot guarantee the lifetime of those instances, nor can we guarantee that your empire will have a spawn point as there are only two warpgates.
Nexus はテストサーバー上にあります。しかし、チュートリアルのようなインスタンスゾーンです。現在、Admin（簡単に言うとサーバー管理者）にインスタンスを作ってもらってワープで入るしか、方法はありません。水曜の夜に Community Clash（コミュニティ主催のイベント）で行われたのが、代表的な例です。