From hong kong to Shenzhen Safri Park?

Luohu border? You can take bus 101 from Shenzhen Railway Station next to the border to the zoo. It is a long journey for the zoo is far away from the border. You can also take subway Line 1 from Luohu to Shenda Station (深大). Then take a taxi or change to a city bus. That can be faster.

How long approximately is the journey?

It takes about 2 hours by bus 101. And if you'll travel by subway and taxi, it needs about 1.5 hours.

Do you know the exact adress?

Qinyuan Road, Nanshan District, Shenzhen. Actually, Shenzhen Safri Park is better-known than its address.

Fastest way is entering at one of the 3 entry points to Shenzhen from Hong Kong (Louhu, Futian and Nanshan borders) and taking the subway to Shenzhen University (??) Then taking a taxi. All up time from Kowloon probably between 1.5 - 2 hours tops.
To be honest, I went to this safari park and it's absoulety depressing. The state they keep the animals in is atrocious. They have workers around the different enclosures offering to pay for meat so you can feed some animals (tigers, wolves, bears, etc). By looking at how skinny some of them are it looks likes they only get fed by the meat the tourists give them - absolutley terrible. If you do decide to go do not see the Tiger show - it's animal cruelty in my books. I walked out after the first 30 seconds. The animals are the ones outside of the cages... pissing, littering and spitting on the ground everywhere. I came out of this safari park depressed and severely disappointed.
That's my 2 cents - good luck if you do decide to go!