Watch.
That's all he'd been doing for years, ever since he dragged himself out through the Hell-gate, to end up in… wherever he now was.
John knew he wasn't a ghost, not in the technical term of the word, never becoming violent or having the ability to move stuff around, nor did he reckon he was in Heaven, for if he was, spending eternity alone wasn't exactly his idea of paradise. But wherever he'd ended up, it came with full-color vision of his boys.
The great John Winchester, he mused ironically - destined to be witness to his sons' agony and ecstasy, without being able to lift a frigging finger to help them.
The death and suffering his sons had experienced had become his own, as painful as if it had been branded on his skin-Sammy dying, Dean in Hell, the demon blood, the Cage, Purgatory. the Mark of Cain. The list was endless, more than any human could be expected to bear and not go stir-crazy.
Yet while he watched his boys bait each other like two carefree kids - the impishness of Dean's grin as he cracked a joke at his sibling's expense, and the adorableness of Sammy's bitch-face as he responded, he felt his heart swell with pride and love.
His sons were truly special, but then he'd always known it.