can you react to a teemo strategist defend trigger after reveal and they choose a unit to deal damage to with a discipline

Yes — but only before the trigger resolves, not after the reveal.

Teemo's target is chosen when the trigger is finalized on the chain, so opponents get a priority window there and can play Discipline (Reaction) to give the chosen unit +2 Might. Once that window closes and Teemo's trigger starts resolving, the reveal-5 and the damage all happen together inside resolution — there is no point in between where you can sneak in Discipline, so you can't wait to see the revealed cards before deciding.

So reacting "after reveal" isn't a legal window; react on the chain (or after the trigger fully resolves, if the chain is still open). This matches FAQ #914 and Rule 355.5.b.