What functional groups are there in caffeine?

The functional groups in caffeine are amine and amide.

The structure of caffeine is

Let's look first at the 5-membered ring.

The two N atoms are part of amine groups.

The ##"C=C"## and ##"C=N"## bonds look like functional groups, but they are neither alkene nor imine groups.

They are both part of the 5-membered system called an imidazole ring.

An imidazole ring is aromatic, like benzene.

Now let's look at the 6-membered ring.

The C=O and N groups look like ketone and amine groups, but they are not.

A C=O next to an N is an amide group.

There are two amide groups in the ring.

So caffeine contains two amine and two amide functional groups.