First, make sure "Log work activities on tasks" in the Project Management section of Project --> Configuration is checked (installs project_timesheet)

The time logged against a task is shown at the bottom of the Timesheets tab. This is the sum of the number of hours in each individual timesheet line.

This information is also available in the "effective_hours" field, but this is only visible to users who have "Time Estimation on Tasks" checked in the Techical Settings section of the Access Rights tab on their user record. By doing this, users also get the ability to set the Initially Planned Hours for a Task and see this, Remaining Hours and a progress bar on the List view of Tasks (progressbar will only make sense if the Initially Planned Hours value is greater than 0.

If you still want to see this on theKanban view, or move it around on the Form view to make it visible without needing to click on the Timesheets tab, you can create your own View to modify the base Views Odoo provides:

Kanban example:

<div class="oe_kanban_bottom_left" position="before">

    <div>
        <field name="effective_hours"/> hrs logged
    </div>

</div>