You can have Marketo create activities on the Lead or Contact that was sent the email for Sent, Received, Opened, and Clicked. This is in the Salesforce settings under Edit Sync Options in the Admin section of Marketo. See screenshot:
I'd be careful with how many you turn on though, that way you're not logging too many activities for the same email on one record. For Example, if all were turned on, and a lead clicked on one the sales emails, that lead would have 4 tasks logged: one closed task for being sent the email, another for receiving the email, a third for opening, and a fourth for clicking.
For alerts (or interesting moments), you can create smart campaigns using these triggers or filters (you can also add a constraint for Sent By if needed for creating separate smart campaign for each rep):
Hi - are you looking for an active notification (such as send alert to sales if email is clicked) or just a place they can check? Marketo Sales Insight itself on the Email tab shows when someone has opened and clicked (and shows a click+ symbol if multple clicks are registered).
If you need an active, real-time notification method I'd +1 to Augie's idea above on sending an alert based on the "Clicks Link in Sales Email" trigger, but that will send the sales rep an alert every single time this happens, and could get overwhelming in larger volumes.
My preferred method here is to send a daily summary to the sales rep of who clicked their sales emails using a smart list subscription. That way first thing in the morning they have a list of who clicked on their MSI/Sales emails the day before, and they can use this to guide follow up.