It depends on what you mean by “see”.
If the sample was large enough you could certainly see it with your naked eye, although you would not be able to say which fatty acid it was.
You could also see a fatty acid under a microscope if you had a large enough sample. But again, would probably struggle to accurately determine what fatty acid it was.
However, spectroscopy and spectrometry are the key! Using IR spectroscopy you could determine what type of chemical bonds are in the sample and hence deduce what functional groups are on the fatty acid chain (e.g. epoxides/alkenes). Using 1H NMR spectroscopy would certainly help too, telling you how many protons (hydrogen atoms) are in each type of environment and giving information such as torsion angles too (using the J values).
I believe one of the most helpful methods, though, would be high resolution mass spectrometry since you can obtain an accurate mass of the fatty acid which will help indicate the length of the chain and will also yield a good idea of how many of each type of atom are present.
UV-vis spectroscopy would certainly give a good idea of the conjugated system (if any) within your molecule too.

I hope this has helped you in some way. Since the question was rather vague, I have tried to attack it from several angles and guess at what the true nature of your question is.

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