Buds will be at the terminal growing point and the seed 'pods' will be on the lower part of the inflorescence.

Remember, the oldest part of that inflorescence is at the bottom....that's where the flowers will set seed first. The top of the flower stalk continues to produce new growth.

Here is a link that might be useful: {{gwi:13370}}

... and the spent blooms usually exhibit a hair-like growth sticking out of the seed head which unopened blooms do not have.

Al

Snapdragons will do a lot better and bloom longer if you cut the whole stem when it gets about 4 inches of spent blooms at the bottom. Yes, it will still have a lot of buds at the top, so use the end of the stem in a bouquet.
But when you cut the whole inflorescence, you promote new growth.
Linda C

The seed pods are also hard: that's another way to tell. I use my index or middle fingernail underneath each one to deadhead: a little sharp flick upward and the pod is off, working from the bottom up. Like Linda suggests, when the flower stalk gets too bare, rangy or scruffy cut the whole thing off. It will send up many new branches from lower down. I do about 1/3 of them at a time, so I'm not completely without snapdragons while I wait (heaven forbid!).