Studies have shown that if you grow up in a language environment where speakers do not distinguish between two sounds, your brain will lose the ability to easily perceive the difference between them. A notable example of this phenomenon is the inability for most Japanese speakers to distinguish between
Jiangsu is an area where the Wu Chinese dialects are traditionally spoken. The Wu dialects, on the whole, do not distinguish between final nasal consonants such as
ng. In many cases, they are allophonic, with the consonant that is actually produced being determined by the vowel that precedes it. This is likely the reason why you currently don't perceive the difference between
jing, because the two syllables have the same vowel when spoken according to the standard. However, it is possible to train yourself to perceive them as separate sounds.
Being able to produce both the
ng sounds is the first step in helping you recognize the difference between them. It may be helpful for you to think of the relationship between the
ng sounds as being similar to the relationship between the
n sound is an alveolar nasal and the
t sound is an alveolar stop, which mean that they are both produced with the tongue touching the alveolar ridge, which is where your teeth meet your gums.
ng sound is a velar nasal and the
k sound is a velar stop. They are both produced with the tongue touching the velum, which is located near the back of the roof of your mouth.
Alveolar sounds require that your top and bottom teeth be touching; therefore, when you say
jin, you should end with your top and bottom teeth touching and the tip of your tongue should be against your gum ridge. However, velar sounds are produced with a slightly open mouth, so in order to pronounce
jing, try to end the syllable with your mouth slightly open; your top and bottom teeth should not be touching and the back of your tongue should be against the back of the roof of your mouth.
Once you've practice being able to pronounce the two distinctly, keep repeating it to yourself and you should be able to start training your brain to notice the difference when you hear it in speech.