I took a test online to knowfind out which English level I was on; tam on. The result turned out to be B2.

Other option: to see which English level I am on.
When speaking English, most people would probably say "to find out what English level I'm on" even though that's technically not correct.
This sentence would also sound natural combining the two sentences: "I took a test online to find out which English level I'm on and I ended up being B2."

It's noB2 isn't bad, andbut I am aiming for C1.

Nothing technically incorrect, corrections are just more natural.

It was a gloomy day here, like my mood after a job hunting online.

NHowever mind, there will be sunshine someday.

"Never mind" sounds like you're saying it was a gloomy day, but you just found out that it was actually sunshine (or it is actually a sunny day).
"However" complements your "someday" because you sound like you don't know when, but there will be sunshine again eventually.

I took a test online to know which English proficiency level I was onat; the result turned out to be B2.

"know" is fine, but you can consider "find out".

It was a gloomy day here, like my mood after a job hunting online.

Alternatively, if you want to keep the "a", you can write "like my mood after a job hunt online".