I am playing a Rogue with the Arcane Trickster archetype.
Are there any Level 5 (or lower) 5e Wizard spells that allow the caster to eavesdrop / spy on / bug a conversation or private event?
The following spells may apply here:
Arcane Eye: Creates an invisible magic eye that can be moved and seen through for up to 1 hour (concentration required)
Clairvoyance: Creates a magical sensor in a place you are familiar with, granting you sight or hearing (your choice) in the location for up to 10 minutes (concentration required)
Scrying: Creates a magical sensor targeting a specific creature. On a failed save you can see and hear the creature for up to 10 minutes (concentration required)
Find Familiar: Creates a familiar you can communicate with telepathically (up to 100 feet), thus it could act as a bug if well hidden
Invisibility: Makes a creature invisible for up to 1 hour (concentration required) or until they attack or cast a spell. (see also: Greater Invisibility allows hostile actions, but has a 1 minute duration)
Polymorph: Turns a creature into a different creature for up to one hour (concentration required). This option changes your ability scores, so your new form must be intelligent enough understand and recall whatever information it gathers. (unfortunate that being a literal bug will not work...)
You could go with...
Find Familiar (Ritual) (PHB Pg.240)
Wizard, 1st level Conjuration
"...While your familiar is within 100 feet of you, you can communicate with it telepathically. Additionally, as an action, you can see through your familiar's eyes and hear what it hears until the start of the next turn."
Clairvoyance (PHB Pg.222)
Bard/Cleric/Sorcerer/Wizard, 3rd level Divination
"You create an invisible sensor within range in a location." "...When you cast the spell, you choose seeing or hearing. You can use the chosen sense through the sensor as if you were in its space"
Clairvoyance pops to mind. Any number of scrying spells and magic items exist. So yes, easily enough. Also such things as a rat familiar (or druid) hidden in the walls. Owl on the windowsill. Detect Thoughts spell, or other mindreading, on a participant. Lots of options.
Arcane Eye, Clairvoyance, Scrying... Dominating one of the members before or after will also work.