Set an alert for an event in a subscribed calendar in iCal

My workaround, annoying as it is, is to copy the subscribed event to my main calendar and set my alerts from the copy.

As of iOS 13, Calendar's Default Alert Time setting will be used for alerts in the external calendar subscription.

• Before subscribing to the external calendar, go to Settings > Calendar, tap Default Alert Times and select the desired alert (in user5118's case, "2 hours before")
• Subscribe to the external calendar as usual

To change the alerts for a subscribed calendar (e.g. from "None" to "2 hours before"), unsubscribe from the calendar, change Calendar's Default Alert Time as described above and then re-subscribe. To unsubscribe from a calendar:

• Go to Settings > Passwords & Accounts > Subscribed Calendars
• Tap the calendar to unsubscribe from and enable Remove Alarms
• Tap Delete Account, and then tap Delete Account again to confirm