I'm fairly certain the PC version has feature parity with the PS4 version except for online multiplayer. Whether all of the above applies to the Xbox One version depends on whether the equivalent updates were pushed out to the Xbox One version. Quests and Event Battles, since they do not permit you to select the officer you are controlling, do not allow for 2P.

2P will control the SECOND officer in the list (after the one controlled by 1P). Dynasty Warriors 8 is a tactical action game that follows the stories of the kingdoms of Wei, Wu, Shu and Jin through the actions of. Also, while maintaining the series intuitive controls, we have included a new Musou Action system where you can experience the thrill of 'one. In Empire Mode, in any offensive or defensive battle in which you can select officers, 2P can press start to join in for that battle (again, look for the 2P Press Start prompt at the top of the screen). Experience the thrill of one versus thousands in an all new open world setting with DYNASTY WARRIORS 9, the latest installment in the series. Event Battles and Quests cannot be done in 2P mode. Look for the '2P Press Start' prompt at the top of the screen. In Free Mode Invasions, Defensive Battles, and Raid Scenarios, 2P can join in by pressing start (or F11 on PC, for whatever reason) at the setup screen where you set the difficulty, officers / marching officer, and so forth. Here's how 2P works on the DW8E, at least on PC after current update (PC version 1.0.3.0):

Dynasty warriors 8 pc xinput controls