The attack bonus cap in Neverwinter Nights is +20, the maximum bonus to attack rolls a character can gain through magic. This includes bonuses on a weapon (enhancement bonus and attack bonus), as well as bonuses from all spells and spell-like abilities. (In particular, true strike by itself reaches the cap.)
Passive feats (ones that a player does not need to specifically activate) do not count towards the cap, nor do combat feats (those activated for a single attack, such as smite evil, as well as combat modes, albeit no combat modes provide a bonus to attack). The remaining activated feats do count towards the cap, as they technically fall into the category of spell-like abilities.