Is a bonus note always taxed at face value?

No. Face value is not automatically fair market value. A note's value depends on its terms and marketability. A freely transferable, well secured, market-rate note from a strong issuer may be close to face value. A subordinated, restricted, below-market, or hard-to-sell note may be worth less.

The EA exam angle is to avoid treating a promise to pay money later as identical to money paid today. If the note is included as compensation, the amount generally follows fair market value at the relevant inclusion date.