Every membership's customer facing purchase page will contain a 'gift to a friend' link, so customer's will see this whenever they are self serving.
You can direct gift inquiries to this page for a more hands-off approach.
However, if you have a customer requesting the link be directly sent to them, or just want to add this link to your website, you can find it by:
clicking Memberships > Subscriptions and Packs > clicking a Subscription
You'll find the gift link off to the right.
Customers will land on a page like this one when the click it.