I use this word a lot, it's very British!
When referring to a person, it usually means the person seems untrustworthy or even criminal: "That man looks a bit dodgy"
When referring to objects, it can mean fake or fraudulent, or sinister: "I just received a dodgy email from a stranger who asked for my credit card details!".
Or just generally bad, for example if you suspect you failed an exam: "hmm that exam was a bit dodgy..." It can even be used to describe food that is going bad: "This milk smells a bit dodgy"
Also, for your question:
What's mean the expression: That’s quite dodgy? because I headed some times.
I would say: What's the meaning of the expression: That's quite dodgy? I've heard it a few times.