There are so called non-regulated professions where you can work without a formal acknowledgement of your skills. If you do not have any certificates, it is a lot harder to get an acknowledgement. It is possible to do a “Qualifikationsanalyse” (qualification analysis) to find out, whether or not the skills you already have are comparable to the skills you would acquire in Germany for a certain job. There may be a specific interview concerning your profession or a test of your practical skills. You can find out more at: https://www.anerkennung-in-deutschland.de/html/de/faq.php