Does replacing a draw with another effect like Notion Thief's ability count as drawing a card for 'whenever you draw' triggers?

When a replacement effect (like Notion Thief's) substitutes a different event for a draw, the original draw event never happens. Under CR 614.1, replacement effects modify or replace events before they occur. Because the draw is replaced entirely, there is no draw for 'whenever you draw a card' triggered abilities to respond to.

Notion Thief reads: 'If an opponent would draw a card, that player skips that draw and you draw a card instead.' The opponent's draw is fully replaced — the opponent never draws, so any 'whenever you draw a card' ability the opponent controls does not trigger. You are the one who actually draws, so your own 'whenever you draw' triggers would fire.

This is governed by CR 614.1a (effects that replace drawing a card) and the interaction principle in CR 603.2, which states triggered abilities trigger when their trigger event actually occurs. Since the opponent's draw event never occurs, their triggers never see it.

Example: Your opponent controls a Phyrexian Arena ('at the beginning of your upkeep, you draw a card and lose 1 life'). You control Notion Thief. On their upkeep, Notion Thief replaces their draw — they skip it, you draw instead. Their Phyrexian Arena's upkeep trigger did fire (it triggers before the draw happens), but any separate 'whenever you draw' effect the opponent has does NOT trigger, because they never actually drew. You would trigger your own 'whenever you draw' abilities.

Note: A draw that is only partially replaced (e.g., drawing two cards instead of one) still counts as draws for each card actually drawn (CR 121.2). But a fully skipped draw results in zero draw events for the affected player.