The problem may well be that you are using C, and libwebkit has C ++ characters. C ++ symbol names will be mutilated compared to what you can see in the included files.
In any case, to answer the question: .la is the libtool library. Usually it points to a .so file:
$ grep dlname libwebkit-1.0.la
dlname='libwebkit-1.0.so'
.so nm :
$ nm -D libwebkit-1.0.so
...
++, -C ++.
$ nm -D -C libwebkit-1.0.so