I know the boy whose father is a teacher.
Here, the underlined clause is -

• Adjective clause:
- যে subordinate clause কোনো noun বা pronoun এর পরে বসে ঐ noun বা pronoun কে modify করে তাকে Adjective Clause বলে।
- অর্থাৎ noun এর post modifier হিসাবে adjective clause বসে।

• Adjective Clause দুইটি স্থানে বসতে পারে।
- Object এর Post modifier. (Subject + verb + noun + adjective clause).
- Subject এর Post modifier. (Subject + adjective clause + verb + object).

• প্রদত্ত sentence-এ “whose father is a teacher” clause টি noun boy-কে modify করছে।

I know the boy whose father is a teacher.
Here, the underlined clause is - Adjective Clause.

Source:
1. A Passage to the English Language, S.M. Zakir Hussain.
2. English Wizard by Live Publications.