• Contact trace employees at WIV and the less secure Wuhan CDC, a BSL-2 lab in Wuhan. And workers at any other labs playing around with coronaviruses in Wuhan. If they don’t want to reveal their contacts then put them in a Re-Education Facility and threaten their families - like you normally do - i'm sure you'll get it out of them.
  
• Cross check with first reported cases.
  
• Locate/interview WIV lab-worker, Huang Yanling, who disappeared suddenly.
  
• Investigate allegations by Chinese and US experts of lax security at both facilities.
  
• Access WIV’s database. According to international protocols, work on novel viruses must be published. Why did it go offline with unpublished material? Is that material relevant to the investigation?
  
• Interview all western scientist who were outspoken in denying a lab-leak was possible (Lipkin, Daszak, Baric, Holmes, Andersen, Rambaut, Garry, Farrar, Fauci, Koopmans, Drosten, Ryan, Tedros, Embarek, Nature/Lancet editors etc). Make all their Covid-related correspondence public. Don't need to rely on China to do that. Give them lie detectors - offer immunity to the first one who spills the beans.

Degree of Difficulty:

Low. It's straightforward detective work. For sure the China-part has already been done by CCP officials.

(Aside: Regarding point 5, as @Billy Bostickson reported, WIV said it’s Database went offline due to "cyber-security issues", which might sound like an excuse, but it makes sense that outside intelligence agencies would have tried to hack it. Did they succeed?)

Conclusion

The weight of circumstantial evidence points to a lab-origin:

• the outbreak happened in Wuhan
  
• there were labs in Wuhan manipulating closely related coronaviruses
  
• biosecurity was lax at these labs
  
• lab-accidents are common

This adds up to the simplest, most logical explanation. Which 'warrants further investigation'.

William of Occam, the 14th century philosopher who championed the ‘keep it simple’ technique of analysis to counter the out-in-the-weeds logic of his contemporaries, will be turning in his grave every time an expert tells us how “painstakingly complicated” it is.
Unsurprisingly, Occam was vilified by the experts of his time.

WHO Investigator Peter Daszak, expert of our time, loves banging on about "evolutionary hotspots", while another WIV/Daszak GoF collaborator, Ralph Baric says the “constant mixing of different viruses creates a great opportunity for dangerous new pathogens to emerge.” What does the computer model say (and William of Occam) when you key in "the constant mixing" going on with WIV’s biological concoction?

Ingredients:

deadly viruses
caged lab animals - (tortured btw)
entitled scientists recombining/evolving/engineering more deadly viruses

Method:
Add human error and stir. Allow to simmer for decades until it explodes.

Serving suggestion:
Deny you cooked it.