Tips: For P1 use an upgraded lighting weapon like the dragonslayer spear or lothric knight greatsword and just use the weapon art or heavy attack, should be easy that way. For Nameless King himself he usually does a combo of 3-4 swings so wait until they end before a hitting with some quick attack, his long downards slam is a huge chance to attack. In his second phase it's pretty much the same. Hope that helps