If you disposed of a security for a taxable gain or loss, you should report this on your return. This applies to gains or 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, such as a high interest savings account, where you’ve already reported your interest income on your return (such as a T5 slip), you probably don’t need to 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.