how does one know if their high-speed dsl is provided by fiber optic or regular telephone lines???

You can call your ISP and ask them. dsl runs through your phone line (split) however prior to traveling to your phone line, it may be running through optical wiring. Best thign is to ask the internet service provider, they should know.

I know for a fact that my Cable internet runs trhough optical wiring (for long distance traveling of data from source to destination)

I have a 6mb download, 800 kbps upload connection.

If you have Fiber Optic lines into your place of residence you have Fiber Optic DSL. If you still have Copper wire in to you home, you have Copper wire DSL.

In order for Fiber Optic DSL to provide you any benifit the Fiber Optic must come all the way to your computer. Any wire in the system will defeat the Fiber Optic benifits.