Sometimes you can find it on the brands website where the PDS are located, but many don't post that information anymore. Another way to know is to check the manufacturer approvals on the back of the bottle.
For instance, if the oil has VW504 approval listed on the back label, you can go this site to see what HT/HS is required to obtain said approval....
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click on Specification until you see a drop down box. Then select from lower portion where daimler, BMW, Porsche and VW are located.
Then click on VW 504
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Here you'll get the HTHS. (also important, the lower the NOACK, the better).
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