J- and CH- are two consonant pairs that are represented by the phonetic symbols /dʒ/ and /tʃ/. Does the /dʒ/ symbol look familiar? This is the same sound as the soft G-, as we covered in Pronouncing C-, K-, Q-, G-.

You will find the /dʒ/ sound in words such as:

judge /dʒʌdʒ/ (notice how there’s the j- sound and the soft g- sound!)
adjust /əˈdʒʌst/
jeans /dʒinz/

You will find the /tʃ/ sound in words such as:

church /tʃɜrtʃ/
exchange /ɪksˈtʃeɪndʒ/
arch /ɑrtʃ/

/dʒ/ and /tʃ/ are post-alveolar sounds, which means that in order to produce these sounds, you have to slightly pull back your tongue from the alveolar ridge and block the airflow from reaching it. As they are post-alveolar sounds and consonant pairs, they are produced in the same place in the mouth. /dʒ/ is a voiced sound and /tʃ/ is a voiceless sound.