Join JSONB column to normal PK column in Postgres
You can use the following query:

SELECT
    *
FROM
    res
    JOIN res_rem_sent ON res_rem_sent.body-&gt;&gt;'resId' = text(res.id) ;


JSON represents all of its contents as text, and that's the reason you have to be very careful on how the UUIDs are converted to text by PostgreSQL. 

Things to take into consideration:


The -&gt;&gt; operator gets a JSON object field as text. 
On the JSON(B) side, you need to represent the UUIDs using the standard form (as explained in UUID Type), so that conversions between UUID type to the JSON(B) text representation produces the same results.
If you want the query to be performant, you need to have at least a (functional) index on the body-&gt;&gt;'resId' part

CREATE INDEX idx_uuid_res_rem_sent ON res_rem_sent((body-&gt;&gt;'resId')) ;
 -- NOTE: the double parenthesis aren't optional
You get the maximum performance if you also have a text index on Res.id:

CREATE INDEX idx_uuid_res ON Res(text(id)) ;
Performance could possibly be improved if, instead of using the text representations, comparisons and indexes are done using UUID representations:

(res_rem_sent.body-&gt;&gt;'resId')::uuid = res.id
In this case, if the conversion fails, you will not be able to insert the data into the table.


DBfiddle here to see a practical simulation of this scenario