Oracle 23c

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

with a(eventdate, userid, traffic, location) as (
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_1', 10,  'A' from dual union all
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_1', 20,  'A' from dual union all
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_2', 10,  'B' from dual union all
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_2', 20,  'B' from dual union all
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_2', 30,  'B' from dual union all
  select to_date('18.09.2023', 'dd.mm.yyyy'), 'user_3', 100, 'A' from dual union all
  select to_date('19.09.2023', 'dd.mm.yyyy'), 'user_1', 50,  'B' from dual union all
  select to_date('19.09.2023', 'dd.mm.yyyy'), 'user_2', 10,  'B' from dual union all
  select to_date('19.09.2023', 'dd.mm.yyyy'), 'user_2', 20,  'B' from dual union all
  select to_date('19.09.2023', 'dd.mm.yyyy'), 'user_3', 150, 'C' from dual union all
  select to_date('19.09.2023', 'dd.mm.yyyy'), 'user_3', 250, 'C' from dual union all
  select to_date('20.09.2023', 'dd.mm.yyyy'), 'user_1', 50,  'A' from dual union all
  select to_date('20.09.2023', 'dd.mm.yyyy'), 'user_1', 20,  'A' from dual union all
  select to_date('20.09.2023', 'dd.mm.yyyy'), 'user_2', 30,  'B' from dual union all
  select to_date('20.09.2023', 'dd.mm.yyyy'), 'user_3', 110, 'C' from dual union all
  select to_date('20.09.2023', 'dd.mm.yyyy'), 'user_3', 120, 'C' from dual
)
select
  trunc(eventdate, 'iw') as eventdate,
  userid,
  sum(traffic) as traffic,
  stats_mode(location) as location
from a
group by
  trunc(eventdate, 'iw'),
  userid

EVENTDATE	USERID	TRAFFIC	LOCATION
2023-09-18	user_1	150	A
2023-09-18	user_2	120	B
2023-09-18	user_3	730	C