SQL>
with employees(department_id,first_name,last_name) as (
select 1,'Scott','Tiger' from dual
)
,departments (department_id,location_id) as (
select 1,1 from dual
)
,locations (location_id,city) as (
select 1,'Moscow' from dual
)
select distinct e.first_name || ' ' || e.last_name as fullname, city,
regexp_replace(regexp_replace(listagg(ee.last_name, ', ')
within group (order by ee.last_name)
over (partition by e.first_name || ' ' || e.last_name),
e.last_name, 'NOBODY'), 'NOBODY, |, NOBODY', '') as collegues
from employees e, employees ee, departments d, locations l
where ee.department_id = d.department_id
and e.department_id = ee.department_id
and d.location_id = l.location_id
order by city;

FULLNAME    CITY   COLLEGUES
----------- ------ ------------------------------
Scott Tiger Moscow NOBODY

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE	11.2.0.4.0	Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production

-- test data
with employees(department_id,first_name,last_name) as (
select 1,'Scott','Tiger' from dual union all
select 1,'Jon','Smit' from dual union all
select 1,'James','Bond' from dual union all
select 2,'Vasily','Pupkin' from dual
)
,departments (department_id,location_id) as (
select 1,1 from dual union all
select 2,1 from dual
)
,locations (location_id,city) as (
select 1,'Moscow' from dual
)
-- you select
select distinct e.first_name || ' ' || e.last_name as fullname, city,
regexp_replace(regexp_replace(listagg(ee.last_name, ', ')
within group (order by ee.last_name)
over (partition by e.first_name || ' ' || e.last_name),
e.last_name, 'NOBODY'), 'NOBODY, |, NOBODY', '') as collegues
from employees e, employees ee, departments d, locations l
where ee.department_id = d.department_id
and e.department_id = ee.department_id
and d.location_id = l.location_id
order by city;
FULLNAME      CITY   COLLEGUES
------------- ------ --------------------------------------------------
James Bond    Moscow Smit, Tiger
Scott Tiger   Moscow Bond, Smit
Jon Smit      Moscow Bond, Tiger
Vasily Pupkin Moscow NOBODY