How Many Moves Deep into Opening Variations Do You Study?

So there are a lot of moves entailed if you study the opening properly.

It's a bit different at the pro leagues - everybody plays book moves. But at an amateur level you have to consider deviation, and for that you have to really work into that positional understanding.  

Studying complete games is far more profitable than studying opening lines anyway.

So "how many moves in... " is not quite the question you're looking for. 

Exactly. Actually that gives me an idea. All those players with impressive opening repertoires, I imagine most of them love going through game databases. It's definitely a fun way to learn openings.

Depends on the opening. My deepest analysis is of the Wayward Queen Attack, particularly the line after 2...Nc6 3. Bc4 g6.
This is the line that I have most familiarity with:

4. Qf3 Nf6 5. Ne2 Bg7 6. Nbc3 O-O 7. d3 d6 8. h3 Na5 9. Bb3 NxB 10. axN Be6

This is the line that I’ve recognized to its deepest:

4. Qf3 Nf6 5. Ne2 Bg7 6. Nbc3 O-O 7. d3 d6 8. h3 >Nb4!< 9. Bb3 Be6 10. Bg5 BxB 11. cxB Nc2+?! 12. Kd1 NxR 13. Nd5 h6 14 BxN BxB 15. QxB QxQ 16 NxQ+ Kg7 17. Nd5 (With a 2N+R Vs 2R endgame on the horizon, I prefer White here, though some may still prefer Black.)

This is the shallowest line that I play:

1. e4 d5 2. PxP QxP 3. Nc3 Qa5 4. d4 Nf6 5. Nf3 c6 (As Black, I genuinely have no clue what to do next. This defense is my weakness, though this likely stems from the fact that I’m not a very good or knowledgable Scandinavian Defense player.)

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Usually, I won’t memorize more than ten moves in depth, as nobody really follows main lines, and I usually have to change my game plans multiple times while on the fly! It helps to watch good grandmaster games, as you will pick up on the main ideas, recurring patterns, and attacks that occur, which, I can assure you, can be better than a thousand memorized lines!

10.

well the last time I posted... All I'll say is my answer has changed. 

Here's an example of a few lines I know fairly deep (and somewhat get the goals of.)

I know a few other lines pretty deep