You forgot to mention that you installed the additional module pg_trgm, which provides the similarity operator. Details:
The basic index you need is a GiST index using the special operator class gist_trgm_ops:
CREATE INDEX trgm_idx ON lcas USING gist (job_title gist_trgm_ops);
This can probably be improved further, depending on missing information ... that you just now added. No more time now, I'll come back to this later ...