This citation looks like the NLM (National Library of Medicine). It could be a variation of Vancouver or maybe Chicago Author-Date format. They are all pretty similar. But I don't think this matches any exactly. That wouldn't be unusual though, depending on where you got the citation from.
I think this begs the question - why do you need to know this? If you downloaded the reference in a common format (like RIS, NBIB, CSV, etc.) you can output it from a reference manager in whatever format you'd like. Good tools for that would be Endnote (paid) or Mendeley (free). If you are stuck with a plain text citation, enter the info manually into one of those citation managers and play around with the output style till you get something that looks similar - that (or some variation) will be the style.
Alternatively, you could start by looking at where you got the citation. Usually (in addition to the downloadable raw data) many databases will give you a choice of preformatted text citations - just pick the one that matches.
If you got the citation off of a publisher website, you can check their preferred format. This will be in the author instructions. I would bet they are outputting the text citation in whatever format they require for authors (or, again, they give you format choices).
If all else fails, you could search for examples of common styles and manually compare. That would be tiresome but might be the best if you don't have any other info.
Depending on what you are trying to do and how much information you have, any of these options would work. Just know that many journals and databases use variations of the common formats, so your citation might not match anything exactly (unless you can find out where it came from). Usually reference managers will come loaded with most common styles and have the option to download variations used by journals, so you can a general template for pretty much any style once you identify it.