You should fill the Box 20 of your T5008s in, so you can reduce the amount of the Capital Gains you are reporting as income. The T5008 - Statement of Securities Transactions may be missing information, so you'll want to obtain and enter as much information as you can in regards to this sale, otherwise you are paying tax on the entire disposition/sell.
The Proceeds (box 21) have most likely been entered, but the Adjusted Cost Base (box 20), may be blank. Many T5008 issuers report only the proceeds because they don’t know your ACB. It’s your responsibility to track your ACB and enter the correct amount in box 20. If you aren’t sure, contact your advisor or broker.
The capital gain or loss will then transfer to the Schedule 3 and 50% will appear on Line 127 of the tax return if a gain results.