German is not mandatory for job seeking. You can apply for some positions in English (some job postings are even in English) and you can also get a work visa for highly skilled migrant or residence permit as a job seeker without demonstrating any knowledge of the German language.
In practice, some companies do hire English speakers but not knowing German will dramatically reduce the pool of potential employers. Unless you have some very specific skills/experience that might convince a large, internationally-active company like SAP or IBM or perhaps a startup to hire you, I don't think you would have much chance on the German job market.