How to combine two queries?
While there's still some missing info (it would help to know if there is only one table, or if there are two tables, the names of those tables, and which columns are held in each), I think this might help.
From what you wrote, it sounds like there are two tables (let's call them 'table1' and 'table2'), and table1 has columns 'id', 'title', 'date', while table2 has columns 'regnumber' and 'title'. Again, if I'm not understanding this, please correct me by providing more information about the tables and the structures of those tables.
It appears that you're missing information linking the 'id' of the event to the 'regnumber' of the venue. I think the best way of linking the event id to the venue regnumber is through a third table (we'll call it 'table3') with two foreign keys: 'event_id' (which would reference the 'id' column in table1) and 'venue_id' (which would reference the 'regnumber' in table2).
Before I move on to the SQL, let's make sure the structure of our three tables looks like the following:

table1: id, title, date
table2: regnumber, venue
table3: event_id, venue_id

With each event 'id' paired with a 'venue_id' in table3, we can move on to writing the following query.
SELECT t1.id, t1.title, t1.date, t2.regnumber, t2.venue FROM table1 t1, table2 t2, table3 t3 WHERE t1.id = t3.event_id;

The reason you'll want a third table is because multiple events will happen in the same venue, and events can happen across multiple venues (like the concert series SXSW).