Can Reminders app set off an audible alarm on my iphone and apple watch to remind me of an event?

You would need to go to Settings>Notifications>Reminders. From there, set a Sound. Make sure that Allow Notifications is turned on and that the iPhone is not on Mute and the volume is turned up. In your Reminders, after you enter a reminder, for you to receive a notification, you have to configure the reminder with a setting under Date or Date and Time for it to generate a sound reminder.

Your profile mentions an Apple Watch SE. If you are using a Watch and have Wrist Detection turned on and the Watch is unlocked, you will receive your notifications on the Watch if the iPhone is locked. If you are not wearing the Watch, or the iPhone is unlocked, then you would receive the notification on the iPhone.

If you have a reminder configured to give you a notification, yes. You would need to either set a date for a reminder, which would then remind you at the default alert time, or you can set a date/time for an alert. You have to configure the notification in Notifications, and then the settings for date or date/time are done when you create the Reminder. This would be similar to creating a reminder for a calendar event. It does not go off like a regular alarm, but you can configure the alert with a longer lasting sound. The standard sound is just like getting a single tone sound.

You're welcome.