For the purposes of activating teamwork feats like Shake It Off and Allied Spellcaster, an Inquisitor with Solo Tactics needs to be adjacent to an ally. The ally doesn't need to have the feat, and as far as I can tell it doesn't even need to qualify. This means I could stand next to a Barbarian and still benefit from Allied Spellcaster, though I wouldn't get the +4 bonus from an ally having the same spell prepared.
How far does this extend?
If the party summoner has a herd of Aurochs on the the field and I stand in the middle of them do I stack up Shake It Off bonuses? Would I get the same benefit from his eidolon? By my logic the answer is still yes.
However, if I have a diminutive familiar (from whatever source) in my pocket do I get a +1 to my saves from Shake It Off, or the bonus from Allied Spellcaster? Would this not count as adjacent, since we share a square? Does the familiar count as an 'ally' for these purposes? For that matter, how would an intelligent item work in this scenario?