If you disposed of a security for a taxable gain/loss you should report this on your return. This applies to gains/losses realized when you sell shares or mutual funds and to income earned when you dispose of securities like mature T-bills.
If this T5008 is for a disposition in a registered account (like an RRSP or TFSA) you do not need to report it.
If you disposed of an interest bearing instrument (e.g., a high interest savings account) where you’ve already reported your interest income on your return (e.g., on a T5 slip), you probably don’t need include this T5008 on your return.
If you aren’t sure, you should call your advisor or broker. Unfortunately, we can’t answer this question for you.