singapore-shenzhen-hong kong

As far as I have understood you will have to travel from Guangzhou to Shenzhen, right? I'm asking this because if you intend to travel from Guangzhou to Hong Kong, you can do it by train using Guangzhou–Kowloon through train departing from Guangzhou East railway station and arriving at Hung Hom railway station in Hong Kong. OK, in case that you have to travel to Shenzhen, you can take a direct ferry from Shenzhen Shekou ferry port (you can reach it by metro) and then from that port to Hong Kong Macau Ferry Terminal (don't be afraid because of Macau name, this is just the full name of ferry port in Hong Kong). You should book your ticket online in advance on CKS - Chu Kong Passenger Transport website. So, this is actually the only easy option to travel between Shenzhen and Hong Kong according to 144 hours visa free rules. Keep in mind that you have to travel exatly with the ferry you have bought your ticket for.

If you don't intend to visit Shenzhen then the Guangzhou-Kowloon through train is your best friend. Keep in mind that you should not confuse it with the high-speed rail which is not eligible for the reason listed below.

If you want to visit Shenzhen then it can be quite tricky, as bus tickets are almost never sold online, while the SZ-HK (and by extension GZ-HK) high-speed rail is not an option because its Mainland Chinese port of exit is located in HK territory and is thus excluded by Mainland Chinese immigration as one of the eligible ports of exit.

Given that Mainland Chinese immigration wants to see the tickets when you are entering the country, you only have two viable options left:
1) buy the Guangzhou-Kowloon through train ticket in advance. After you have entered China, buy a roundtrip Guangzhou-Shenzhen rail ticket (can be on high-speed rail in this case because you are not leaving Mainland China). When done visiting Shenzhen, return to Guangzhou to depart to HK on the through train.
2) buy the following two tickets in advance: a one-way rail ticket from Guangzhou to Shenzhen, and a ferry ticket from Shenzhen to Macau. After your arrival in Macau, you can buy the other ferry ticket from Macau to HK. (There are ferries going to HK from Shenzhen, but those tickets can't be purchased online.)
Keep in mind that you also have the 5-year tourist visa option when holding a Brazilian passport although it most likely can only be obtained in Brazil.

which company for the ferry to macau?

Turbojet.

As far as I have understood you will have to travel from Guangzhou to Shenzhen, right? I'm asking this because if you intend to travel from Guangzhou to Hong Kong, you can do it by train using Guangzhou–Kowloon through train departing from Guangzhou East railway station and arriving at Hung Hom railway station in Hong Kong. OK, in case that you have to travel to Shenzhen, you can take a direct ferry from Shenzhen Shekou ferry port (you can reach it by metro) and then from that port to Hong Kong Macau Ferry Terminal (don't be afraid because of Macau name, this is just the full name of ferry port in Hong Kong). You should book your ticket online in advance on CKS - Chu Kong Passenger Transport website. So, this is actually the only easy option to travel between Shenzhen and Hong Kong according to 144 hours visa free rules. Keep in mind that you have to travel exatly with the ferry you have bought your ticket for.

I will add just several details, especially regarding the eligible direct ferry service between Shenzhen and Hong Kong, that will complement great advices offered by John Doe.

As far as I have understood you will have to travel from Guangzhou to Shenzhen, right? I'm asking this because if you intend to travel from Guangzhou to Hong Kong, you can do it by train using Guangzhou–Kowloon through train departing from Guangzhou East railway station and arriving at Hung Hom railway station in Hong Kong. OK, in case that you have to travel to Shenzhen, you can take a direct ferry from Shenzhen Shekou ferry port (you can reach it by metro) and then from that port to Hong Kong Macau Ferry Terminal (don't be afraid because of Macau name, this is just the full name of ferry port in Hong Kong). You should book your ticket online in advance on CKS - Chu Kong Passenger Transport website. So, this is actually the only easy option to travel between Shenzhen and Hong Kong according to 144 hours visa free rules. Keep in mind that you have to travel exatly with the ferry you have bought your ticket for.

Thanks for this excellent addition.

thanks for that! hong kong macau ferry is located in macau, right?! and the tickets will be avaiabld only 30 dias before?

Hong Kong Macau ferry terminal is in HK, not Macau. From the website it seems like tickets are roughly available between 1.5 to 2 months before departure. Keep in mind that the departure is from Shenzhen Shekou and arrival is at Hong Kong Macau terminal.

Oh, thanks for all the answers! Now it's very clear!!

Does CKS offer the online ticket? If not, does the voucher work for applying the 144hour and to show before my trip to mainland china in the airport, as I well understood it is needed? Thank u

I don't have any information about CKS. You can contact with them for more details.

Just Google the name of CKS provided to you by Janez. Same with Turbojet.