אמור תמיד את האמת.

English Translation

Always tell the truth.

is this supposed to be אומר תמיד את האמת ?

It’s correct as it is. The first word is the masculine singular imperative (here with vowels):

אֱמֹר
(emor)

When looking for the verb forms to which an unvoweled word could correspond, the site pealim.com is useful. See, for instance:

אֱמֹר!‏ ~ אמור!‏