Below is the entirety of the Melee entry for the NPC in question:
Melee +1 dagger +10 (1d4+4 plus poison), or +1 dagger +8 (1d4+4 plus poison) and masterwork dagger +7 (1d4+1 plus poison)
When looking at a weapon entry, the first number (bolded above) prior to the weapon's name is usually the weapon's enhancement bonus. You don't take this number into account when rolling for an attack - its just for your reference. The second number (italicized above) is the total attack bonus for that particular attack. That would be what you add to your die roll to determine if the attack hits.
As for where these modifiers are coming from, they are calculated based on the creature's statistics, just as they would be for a player character. For this NPC, it has a +5 base attack bonus, +3 strength modifier, weapon focus with daggers for a +1 and a +1 enhancement bonus on its dagger, for a total of +10.
This particular stat block also provides an alternative option when attacking, signified by the "or". It lists two attacks, one with a +1 dagger and the other with a masterwork dagger. Since these have lower attack bonus and they're listed separated by an "and" you can determine that they're the NPCs attacks when two-weapon-fighting (you can also guess this from its feat list lower in the stat block). When full attacking, the creature can make one attack with its +1 dagger (at a +8 bonus) and one attack with its masterwork dagger (at a +7 bonus).
Note that the stat block has an error and the masterwork dagger's attack bonus should be 1 point higher each time it shows up.