How To I have an HISENCE 55INCH UHD SERIES6 and there's no headphone jack? What do I do

Without the full model number it's hard to give you an exact answer. Some models that come up in searching have a headphone jack on the rear. Check for that.
If there is none then you will need a headphone amp or bluetooth transmitter with optical audio input.
Check the TV manual on how to use that audio output.
 

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