Ok. Does Target Lock allow you to reroll any or your dice? Or just the blank ones?

Any dice that have not been previously rerolled (such as by the upcoming card Elusiveness)

Thats what I thought. But a player who has been playing far longer then me thought differently. So we went with his ruleing. Oh well. Was not a game changer.

From the rulebook, page 11:

Spending Target Lock Tokens
If the attacker has a target lock on the defender, he
may return his pair of assigned target lock tokens
to the action token supply to choose any number of
attack dice and reroll them once (see “Combat Phase
Example” on pages 14–15).

Nothing in there about the dice having to be blanks.

I guess he's been playing it wrong far longer than you have.