It is entirely possible to spend most/all of your career doing significant, useful work, with only minimal knowledge of algorithms and data-structures.
The minimum level of knowledge for algorithms and datastructures, in order to be successful, will require you to:
- be aware of most of them (including reading up on new ones occasionally as they come out)
- know where to find good, tested, working implementations
- be able to compare algorithms and their usefulness
- be able to correctly copy one from an open-source example to your specific environment, with a small bit of tweaking
There is no *maximum*. If you want to, you can take your study to the PhD level and beyond. It's usefulness is directly related to the kind of jobs that you're interested in having, and to which kind of work you find most interesting and rewarding.
That said, as a rough (but not absolute) guideline, the more low-level, more resource intensive and less automated the language, framework, and application that you're working on will be, the higher the required skill level when it comes to algorithms, and data-structures. For example, implementing Ukkonen's algorithm in assembly will likely, but not necessarily, mean you'll want a masters' level understanding of the algorithm and data-structures involved.
In your specific situation, going from a Java development background to working on the iOs, all other things being equal, expect a slightly higher demand on your general understanding of algorithms and data-structures. You'll want to be able to run efficiently on a device with fewer available resources. Also, expect to add a couple of new categories to your arsenal - most notably, you'll want to know more about memory management.