COMPULSORY REGISTRATION

What type of agent?
insurance agent?

What will be answer for different agents?

As per Definition of u/s 2(5) : Agent is person engaged in supply or receipt of Goods/Services on behalf of other person who generally called as "principal"
So as per above , importantly, the essential is that Agent should be engaged in any business of some other person .
So even though if the "principal" is Un-registered, the Agent is compulsory required to get Registration.
Note : The agent who are not selling Agent do not cover under defination of Agent .

For kinds of agent kindly refer Circular No. 57/31/2018-GST & 73/47/2018-GST

But I read that agent is liable to be registered only when the supply is taxable and the supplier is a taxable person.
For example - when agent is for an agricultural purpose , he is not liable to register , as the supply there is non taxable and principal is not liable to tax.

yes correct , if he is engaged in supply of exempted goods then cover under section 23 of cgst act, hence section 24 cannot override section 23.

but its matter of ligation , many aar ruling in this case was if person satisfy the condition in section 24 provided that the condition of section 23 also satisfy need to obtain registration mandatory

https://youtu.be/32jnJSfhAyA