I've transcribed the lexicon and gave it to Signus.

Here is where I need help.

He is supposed to give me some sort of blood extractor but all he says to do is to wait. The guide mentions nothing about him telling me to wait.

This is the second time I've tried this quest. The first time, I gave the lexicon ages ago and he still has no new dialogue options, even after almost 100 in-game hours. Now this time, he is doing the same thing. All objectives are complete and I can't progress in the quest because he never has anything new to say. I've already beaten the Main Quest on my first character and he has no new dialogue options after a very long time playing.

PLEASE HELP!!!

This is a spoiler, but anyhow:

All I can say is re-load because I haven't heard of or experienced this.

i don't know how to use the spoiler button but you need to be past a point in the MQ before you can move on

Click on the third icon from the left, a tool tip will say "Special BBCode"
Select Spoiler from the dropdown menu. You can also use "spoiler" and "/spoiler" both inside brackets and not quotes, to manually do it, and type the spoiler text in between.

EDIT: And yeah, questions about quest specifics should be asked on the spoiler board instead of GD.

Have you completed the MQ on the affected character?

You mention "second time" you've tried this and that you've comepleted the MQ on your 1st character so I'm not sure on which character you're trying Discerning the Transmundane now. There's a known bug if you completed (actually almost completed) the MQ before Discerning the Transmundane.

You need to be level 15 before the quest will continue.