How do you informally say “I took a picture of this”? Is “I took a shot of this” gramatically correct?

Yes it's grammatically correct and the phrasing is fine. There are a few informal ways to state it as others have suggested.

I would assume it would be something more along the lines of "I snapped a pic of this".

I "Captured this!"

Saying “I took a shot of this” couldn’t be misinterpreted though, you could say “I snapped a shot” to emphasize what you’re trying to bring to light.

Yeah, but it's not that much more informal. Either are suitable, really.

Possibly....”I took a shot of this!” 😊

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Just one, of my many, great captures. 😁

I snapped a shot.

I took a wee snap 👍️

Ye

It was there- I "shot it", "I snapped it", "I was dumbfounded-had to get it!" As long as you get the image you want is what counts.

In a photography course I learned we don't "Take" pictures, we "Make" pictures.