In order to lock the opponent out of drawing cards with lore broker and Notion Thief's ability, you must activate the looting effect in response to them drawing a card on their draw step, so they immediately loot, not drawing the card for the loot, and discarding the card they just drew, with you also drawing an extra card due to Notion Thief's ability.
I would rephrase that a little bit because it might be a bit confusing for newer players. The way its phrased here would suggest that you want to activate the looting before they draw their card for the turn. Obviously, you can't respond to the normal card drawn in the draw step, as drawing your normal card is not a trigger and the draw step starts with players drawing a card without anyone getting priority.
I know what you mean and the combo is correct to work here, but I would just say: Activate the loot effect in your opponents draw step.