How Many ..
I'd guess you don't know. I don't know those things about my house, either, and I likely know more about my home than most folks do about theirs. And it's OK that I don't.
There is such a plethora of witnessing "plans" floating around ..... so many books have been written inviting you to read them .. so you can witness without fear ... that folks may be under the impression that there's something else they need to know before they can witness properly. And that thought is simply wrong. The thought that there is anything to fear in witnessing for Jesus.
The one part of your salvation experience that no one can argue with is what actually happened to you. Joseph Garlington, IMHO, spoke well when he said "A man with an experience is never at the mercy of a man with an argument." As long as it passes the test of Scripture ... hey, we don't always get it right, you know ... then you know what God has done in your life!
In my case, I know what happened when I was 11. When my dad reminded me of what I had learned in VBS ... that if you believe in Jesus, you go to Heaven when you die ... and I care not how many atheists line up to tell me otherwise, it would not change one bit of what happened to me then.
Or the miraculous things God has done in my life, since then.
When we're talking about witnessing about our faith, in church or Sunday School, I'll frequently ask folks to describe their homes. We'll usually hear about square feet, bedrooms and baths, siding, garages, all the usual things. After that, I'll ask about nails, shingles, furnace BTU's, feet of piping in the plumbing system .... stuff like that. Folks normally say they don't know ... my usual response is that I don't know that stuff about my house either, and it doesn't bother me that I don't.
My big point comes last: that I would never let what I don't know keep me from telling what I do know! Just like they didn't let what they didn't know about their houses keep them from telling us what they did know.
Why would we let that happen, with reference to telling others about our faith, when what we do know ... what has happened in our own lives ... is the part others cannot really dispute!
Especially when the things we do in the Kingdom work are the only things we will still have, when we get to Heaven?