How many baptisms does it take to be a Quaker?
If you're talking about something that involves water, the historic answer is none.
The official answer, as given by the Faith and Practice statements of many Friends bodies, is that there is one baptism given directly by the Spirit. That is all that is needed and it doesn't involve water.
The answer from my experience with God is that it takes a lifetime of baptisms to be a Quaker.
I grew up in Baptist churches. My life was blessed by parents and other people who loved Jesus and shared their stories and the stories of Jesus with me. When I was nine years old I responded to an invitation for salvation and a few weeks later experienced full immersion in the baptistry of that church.
As a nine year old, I wasn't very aware of the theology involved in being baptized, but I knew that getting all wet in front of all those people marked a transition. I had made a public statement that I was a believer in Jesus.
And then I spent ten years or so pretty much ignoring Jesus.
When I was twenty I went through a second baptism. I got wet this time as well, but there was no water involved.
Some friends and I invited ourselves to a party one Saturday night. I don't know who the host was and didn't know very many people there, but it was loud, crowded and fueled by alcohol. In the course of the party, I stepped across a line with my friends that I shouldn't have. My good buddy Ervin then proceeded to pour a bottle of beer over my head.
I stopped. And I knew that God was reaching into my life. God used that bottle of beer to bring me to the place where I knew I had to make a choice -- I could continue messing around with life and ignore God, or I could take the claims of Jesus seriously. It was a very clear and unavoidable choice in front of me.
Paul describes baptism this way in Romans 6:3-4:
Or don't you know that all of us who were baptized into Christ Jesus were baptized into his death?  We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life. (NIV)I was stopped dead in my tracks by that beer being poured over my head. It was a baptism -- I experienced being buried with Jesus and being raised from the dead. My life was new.
At about the same time I was starting to hang around different kinds of Friends. I became part of a Friends Meeting and discovered people who loved others and took their relationship to God very seriously.
And they taught me two new ways of being baptized--
In worship -- being buried with Christ in worship, so that his living presence can continue that job of making me new. It's a process that started when I was a child and it will continue for a lifetime.
In service -- allowing my wants and needs to be buried with Christ in service, so that he can use me to be a small part of creating something new in our world.
It takes a lifetime of baptisms to be a Quaker.