> Is Dragon book still relevant?
No, not at all, the teachings and techniques have been surpassed since four decades or so.
The algorithm LALR is flawed, it only works for a subset of CFG instead of all. That alone is already a death blow. If you want to try out BNF grammars in the wild, it is nearly guaranteed that they are complex enough for LALR to shit itself with S-R conflicts.
The technique of generating and dumping source code is awkward and the reasons that made that a necessity back then are no longer relevant. A good parser is simply a function call from a code library.
The technique of tokenising, then parsing in a second pass is awkward, introduces errors and again the reasons that made that a necessity back then are no longer relevant. A good parser works "on-line" (term of art, not meaning "over a computer network" here) by tokenising and parsing at the same time/single-pass.
The book precedes Unicode by a long time and you will not learn how to properly deal with text according to the rules laid out in its various relevant reports and annexes.
The book does not take into consideration the syntactic and semantic niceties and features that regex have gained since and thus should definitely also be part of a grammar parser.
> recommend any other learning resources
Depends on what your goals are. For a broad and shallow theoretical introduction and to see what's out there, browse the slide decks of university lectures for this topic on the Web.