What is the expression?

The phrase is certainly common. Speaking of which, what do you imagine is wrong with it?

I do not know why, but it sound weird. In which context would you use this expression? Thanks a lot

'Gee it's been hot today, almost 40 degrees. Speaking of which [I.E. SPEAKING OF THAT TOPIC], did you hear that many Frenchmen died in 40-degree heat last year?'

'I saw your brother crossing the street yesterday. Speaking of which, he still owes me thirty dollars.'

'Everyone's expecting a close election again this time. Speaking of which, I read that they are changing the vo

I've just read that the interjection "gee" is an euphemism for Jesus (Merriam-Webster's D.)
New for me.

Historically, yes, Elena, but it is now used as such by very few. For most, 'gee' would be more accurately defined as 'oh', 'my goodness', etc.

Thanks.

This time, Merriam-Webster's didn't explain to me the meaning of "et.al."
Please?

Few minutes later.
Now yes:

Etymology: Latin et alii (masc.), et aliae (fem.), or et alia (neut.) = and others

(Merriam-Webster's D.)