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). 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). Press F12 to clear all of the preset controller configurations so you have a blank slate to start adding buttons Then map the buttons to the following: Action. Gamers can save data from the PS3 version of Dynasty Warriors 8 and use it for their Vita or PS4, and cross-platform play lets them enjoy co-op action with.

Go to Options, Controller, and P1 Settings. Event Battles and Quests cannot be done in 2P mode. So mapping the controls is pretty simple.

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 save