A complete answer to your question requires a bit more context than you have provided, but this is a common question, so I will make some assumptions. :)
If this is a page using Calendar:Events tag to display complete/more info about an event, and you are linking to this page from a page such as a full month view calendar, we'll often use this workaround:
In the full month view template (using Calendar:Cal), we'll adjust the link for the title of the event to have this extra code:
{if event_recurs}{event_start_date format="%Y/%m/%d"}/{/if}
So, the complete code for the title link would be:
<a href="{path='calendar/events'}/{event_url_title}/{if event_recurs}{event_start_date format="%Y/%m/%d"}/{/if}">{event_title}</a>
What that will do is add some fake date values into the URI, which can be retrieved later ;)
Then, in your Event detail page (using Calendar:Events tag), you would have something like this code:
{exp:calendar:events
event_name="{segment_3}" <!-- grabs URL title from 3rd segment, where we sent it -->
event_limit="1"
dynamic="no"
}
<h2>{event_title}</h3>
<p>
{if event_recurs}
{exp:calendar:date
base_date="{segment_4}-{segment_5}-{segment_6}"
output_date="today"
}
{date format="%l, %F %j"} @ {event_start_date format="%g:%i%a"}
{/exp:calendar:date}
{if:else}
{event_start_date format="%l, %F %j @ %g:%i%a"}
{/if}
</p>
{/exp:calendar:events}
You'll see that we're using the date values from the URI that we passed on from the previous template, and now feeding them into the Calendar:Date tag, and telling it to parse those segments into a formatted date. We then use the {event_start_date ... } variable, but only for the time parsing.