Wealthsimple offers both Joint investment accounts and Joint Smart Savings accounts. Each of these have tax implications as they are non-registered accounts (more information can be found here).
Each account receives one of each applicable tax slip (a full list can be found here) and is typically issued in the name of the primary account owner's name, though a copy of the slip can be downloaded from either owner's Wealthsimple profile.
Typically we recommend that the tax information on these slips be filed under the same name as they're issued (i.e. the primary owner), but co-owners do have the option to split the income earned within Joint accounts in the way they prefer (e.g. 50/50 split). If co-owners decide to split the income, the responsibility lies with them to decide how and to claim the correct amounts on their personal tax returns!