How do you pronounce Erjie?
I'm assuming that this person's name is spelt according to standard Mandarin Pinyin.


[jie] is pronounced something like "jyeh".
[er], in the International Phonetic Alphabet, is /ˀɤɻ/, made up of the close-mid back unrounded vowel and the retroflex approximant. Speaking for an American English audience,


A fair approximation of the close-mid back unrounded vowel is IPA /o/, which is the vowel in the English word "go".
The retroflex approximant can be given as the consonant in the English word "red". See http://www.lel.ed.ac.uk/research/gsound/Eng/Database/Phonetics/Englishes/ByWord/Word_075_red.htm and listen to "Standard American".



Putting this together, and ignoring the tones, you should be pronouncing the name like the following:


[er] - https://www.youtube.com/watch?v=T8AOX0FssQk
[jie] - https://www.youtube.com/watch?v=-m6bQVJtPT8


(The sound plays at about 4 seconds in both videos.)