Can a tourist visa holder apply for woking visa while in Singapore

After you find a job, the employer (not you) applies for your work visa (EP, S-Pass or WP).
This is possible at any time, regardless of where you are and on what visa. The application process can take between a few days and several weeks, depending on how fast your home country's authorities cooperate in verifying your credentials. (Yes, they will contact Algeria and check everything you said in the application, because there were so many fakes in the past!)

hello beppi and thank you very much for the valuable infos you just gave me, really helpful

It's not as straightforward as having the right credentials. MOM will also review the company who you are applying for your work visa. They will assess how many foreigners are working there in relation to Singaporeans as well. Also every foreigners vwork visa works on a point system. Your assessment will be based on your nationality, professional qualifications and your value to the organisation who is sponsoring your application. It's on a case to case basis. Usually professions in biochemistry, medicine, engineering carry is easier. If your are a director or in senior management again you get more points!

Hope this helps