These photos show how we learned to use the automatic needle threader on the Juki TL-98Q.

Lower the presser foot and make sure the needle is in highest position.  Then lower the needle threader lever.  Two metal arms will swing around and position themselves on either side of the needle. When the needle threader lever is fully down, a small hook should have been pushed through the eye of the needle.  This is where we had the most trouble trying to get the needle threader to work.  At first, the hook wouldn't go through the needle's eye.  Gentle pressure on the back of the needle threader, pulling it forward, allowed the hook to go through the through needle's eye.  If the needle moves when you lower the needle threader, the hook probably hasn't gone through the eye. With the hook in place, the rest of the instructions in the TL-98Q manual are easy to follow.  
The thread goes into the top needle threader guide and under the lower guide (the part that looks like a little shovel.

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Then the thread is passed over the bar behind the needle threader. Pull the thread down behind the metal arm on the far side of the needle, across the front of the needle, and into the plastic guide under the needle threader hold-down button.

Here is where we kept going wrong until we discovered the hook wasn't positioned as it should have been.  Notice that in this photo, the hook isn't through the needle's eye.
If the hook is in position to grab the thread, keep a slight tension on the thread as you release the needle threader, and the hook will pull the thread through the needle's eye as it retracts.

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When the needle threader is fully released, the thread has been pulled through the needle's eye.

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