3-level Abjuration
Here is another statblock as a demonstration
To those who need to hear it: it is currently impossible for a block designer to create the ability for a user to have statblocks within statblocks. The only reason a few exist is that they use systems not normally available. Community sheets CAN NOT have this feature in the current system. I'm hopeful this will change.
Well to re-iterate what I already said in the help channel: You are approaching it from the wrong end. I don't know which system you intend to use, but the most recent 5e sheets for example already give you the option to give a character a spell list via a dedicated input for block IDs that will embed the spell sheets in the character sheet. If the sheet you are trying to use does not have this feature, it's because it was coded that way. If you want it to have that anyway, you have to modify or create it on your own. All sheets on WA are coded by community members so I suggest you should make yourself familiar with the sheet creation process to understand why what you're asking for here is already possible and has been done many times.
Certain blocks can be attached to certain templates already. That system is robust and usable. There is absolutely no reason to do this. And further creates the risk of infinite loops would have to be handled.
I am a bit on the fence with this one. I think in your case where you specify to provide a list of spells to players from a single(???) statblock you would just have more luck @ the spell itself with said article containing it's appropriate stat block. I think this would save clutter and not look like a giant mess otherwise. It sounds like you want to keep it centralized so if you update one you update all? Perhaps a link to a meta-article containing either statblock or article block of said spell would be best in this case. Perhaps in your use-case using statblocks to list all KNOWN spells of NPCs would not be advantageous if you plan to change them consistently. If it's some form of evolution maybe you would benefit from using the "Make a duplicate..." feature at the bottom of the statblocks. Traditionally NPC/Bestiary usually work by giving them a Spellcasting-like trait with a level, including a list of spells they know by level. Something like: Spellcasting: This creature is a 2nd level spell caster. It's spell casting ability is X. The creature has the following spells prepared (Perhaps change to known in your case) Cantrips (At will): mage hand 1-st level (2 slots): shield, thunderwave etc.