Where does the 10th dwara lie and how can it be opened?

The 10th dwara is not to be found at some particular place. It is a state of being. Had it been present at some particular place, the scientists would have told about it since long and also would have succeeded in opening it with their very small and delicate instruments. However, nothing of the sort has happened.
That State attained by transcending all the three states —Sushupit, Swapan and Jagrit` (Deep sleep, Dream and Awake). In the awakened state, it is the Karamendreyas (Organs of action) and Jnanendryas (Organs of senses) that function. All the actions are performed with the help of air movement in the body. This air has been directed from the navel-Manipura. From where have we been receiving this air? The air is present in the atmosphere. The basis of our awakened state is by this very air. We breathe even during our sleep. It means, one need to move out of this very breath. Man breathes through the Ida and Pingla nerves. This breath enters into the navel automatically. It is just like the water that flows from the higher level to lower level. From the navel the breath divides into 10 parts. These parts perform different kind of jobs like hearing, walking, applying force and the like.
In order to stop the supply of air, the Sushumna is opened by closing the Ida and Pingla. Then the whole physical system ceases to function. The 10 different kinds of air are drawn together from the body by concentration. Because of it, the organs stop performing their respective functions. This stage is also called as Shunya Samadhi. Reaching this stage is not an ordinary thing. For this, one has to move out of the awakened state. The Ida has to be absorbed in Pingla so that the air, instead of moving down in to navel, moves upward.

Ulta Jaap Japa Jab Jana, Balmik Bhaye Brahm Smana  

Valmiki became Brahm like only after reversing the
airs in the upward direction.
The Mind will try to create all sorts of hurdles but the devotee has to keep the concentration fixed. This is because the direction of the breath can be reversed with the power of concentration alone. The breath has got accustomed to move towards the navel. As such , the body doesn’t get emptied all of a sudden. The Mind, in a very clever manner, tries to divert our attention. It will make us remember some incidence that has no connection at all with our present concentration. That is why the guidance of the Guru is needed at each step. In this way our Mind has closed the 10 dwara.

Sushman Madhya Basey Niranjan, Moonda Dasvan Dwara  

God-Niranjan has occupied the place in the Sushman
nerve and has thus closed the 10th dwara.

Gaflat Nehin Tahan Hosheyar Dekhna  

Not laziness but it is the alertness that is needed
there.

Tiktaki Chand Aur Chakor Ki Lagi Rahe  

The concentration like that of a Chakor ( a bird ) for
the moon is needed.
All our labor will be lost if we allow our con-
centration to deviate for even a moment.

Tahan Silhali Gail, Chadoon To Gir Gir Padoon  

That is a very slippery place. That is to say, it is a
very uphill task. One can fall at any moment.
The Activity of the Mind never stops. It makes us remember only such things as irritate us much. The devotee who doesn’t fall a prey to the tricks of the Mind, begins to understand its moves. If you continue your journey, you will be able to experience your Soul. This state is called as the Turiya state where the Mind prevents the devotee from entering. In short, by default it doesn’t let anyone enter into the inner world.

Munn Cheenhe Koyi Birla Yogi  

Only some rare Yogi can understand the Mind.
Remember! It is the breath that has made the Soul
feel itself like a body. Therefore, the devotee has to move
overcome this breath.

Marte Marte Jug Moa, Maran Na Jana Koye  

The worldly people have been dying but none knows
what the real state of death means.
Nanak Dev Ji says—

Jeevat Mariye, Bhavjal Tariye  

Salvation during the very lifetime makes one cross
the worldly ocean.

Just see! The devotee wants to escape but the Mind motivates him to remain entangled in the world itself.
No problem will appear before concentration. There is warmth in the breath. That is why the body becomes cold after death.
In short, The breath and the Surti (Concentration) have to become one. When the whole body reaches that state of cease, a sense of fear overtakes the devotee. At first, it will appear as if the hands have stopped functioning and then it will appear as if death is approaching. The Mind, in a clever way, will instill this very thought of death in the mind of the devotee. When the devotee thinks he is really dying, he thinks of postponing the idea of fixing concentration to some other date. It is not an easy path. After this, the jiva reaches Shunya and then the 10th dwara opens.

Sheesh Utare Bhuin Dhare, Taper Rakhe Panv  
Kahain Kabir Dharma Dass Se, Aisa Hoye To Aav  

Sahib Kabir says that only a devotee, who crushes
his ego, can accompany him.