How exactly does a person jump from dogmatic Christianity to gnosis? Because it is an extraordinary leap. Think about it. You're taught in dogmatic Christianity that Jesus literally died for our sins, Noah built an Ark because Jehovah was angry at the rest of humanity's sins(except for one family's), it's perfectly alright to incestuously sleep with your father if the goal is to continue the human race, Jehovah/Allah looks kindly upon those who murder others as long as they're infidels, and a myriad of other heinous concepts....
.... doesn't it seem a bit much to wrap your head around? Doesn't it seem unkind? If you can convince yourself that Jehovah of the New and Old Testament isn't seriously schizophrenic and in need of a therapist of the highest caliber then you're nowhere near the path of knowing what reality is. And that is what gnosis means. Knowing. Rationality is a must in attaining gnosis. A person who likes to be spoon-fed what to think will never attain gnosis because that is the antithesis of what the good god wants for you, which is to Grow Up and reach your potential Adulthood.
But what if you are on that path? What if you do find all these bizarre contradictions in the Bible too much for your heart to handle? What if you don't feel loved by God so much as enslaved? Then you know that you're on your way to change. If something just doesn't feel right with what you read in dogmatic texts like the Old and New Testament then you're in for a wild journey.
Let me first make clear to you that there is no written text you will ever find which will give you a step by step set of instructions on finding gnosis. It doesn't exist. It is a 100% personal experience which is personalized by ... guess? Ourselves. Our own choices. It's true. No one ever wakes up and falls into a state of gnosis when the day before they were speaking-in-tongues-Pentecostals. Or Baptists. Or Jews. It just doesn't happen.
For some gnostics they claim that they turned their back on dogmatic Christianity/Hinduism/Islam/Judaism/etc because of this inner voice which told them that all is not as it seems when they looked at the big wide world around them. They began searching for answers by investigating any and all religions. Some people immerse themselves in meditations, yoga, breathing exercises, and even occult practices involving deities which their childhood religion forbade researching lest it taint their minds. Others simply hop around to different church denominations, never happy but always feeling like they're on the cusp of finding what they're looking for. Most turn into rabid book worms. Gnostics are generally well read folks, as a rule. We have to be in order to educate ourselves on our choices instead of blindly following others like sleepy sheep. Anything from Valentinus to Plotinus to Plato to Shakespeare... you'll find it all on our bookshelves, even if there is an increasing number of very good modern gnostic authors to choose from.
There is no One Path to get on the path to gnosis. Every person's journey is unique and we all have a childhood of sorts which we must go through in order to find the right path to gnosis for us. Exploration is encouraged!! There are bits of gnostic wisdom in all religions to be found. However there are common themes in these journeys. Something nagged at them in the back of their mind and they couldn't in good conscience continue practicing a religion they had no faith in. The tide turned, that person changed, and their eyes opened. They realized that they were enslaved by the material world and that their spirit was in fact a separate entity from their body. They no longer identified with the material world and saw its many sparkling lures for exactly what they are: a means to trap our minds in an empty oblivion of entertainment. The truth is that the material world is meant to entertain us away from thinking about the very nature of ourselves.
The good god wants us to be loved and feel loved because we deserve it. It is our birthright. Not because we've jumped through so-many hoops that it satisfies some bent egotistical mania Jehovah possesses. Because the good god is not egotistical in any way. He knows what's what and doesn't require our blind subservience.
The type of relationship you will end up having with the good god/the All/pleroma is one of confidence, enduring endearment, questing and yet always finding. When we 'grow up' and find the good god we realize just how little we needed the pomp and ceremony of the fearful branches of Christianity of our youth. Our gnostic childhood when we first find him is quite exciting!!!
I encourage you to use Google and your own curious mind to ferret out those answers you've been looking for. Wikipedia is gnostic-friendly and so is Amazon and Barnes & Noble. Just don't cross your fingers that you'll find what you're looking for in your local Christian Bookstore. Think outside the box.
Key words to use in your quest: gnosis, gnostics, gnostic writers, Valentinus, Nicene Council, Irenaeus, Gnothi Seauton, Nag Hammadi Scrolls, Cathar, Gospels of: Thomas, John, Baruch, Mary, The Secret Gospel of James, Pleroma, The All, Gospel of Truth, Gnostic Bible.