Connect to the primary server and execute:

    repmgr=# SELECT * FROM pg_stat_replication;
    -[ RECORD 1 ]----+------------------------------
    pid              | 19111
    usesysid         | 16384
    usename          | repmgr
    application_name | node2
    client_addr      | 192.168.1.12
    client_hostname  |
    client_port      | 50378
    backend_start    | 2017-08-28 15:14:19.851581+09
    backend_xmin     |
    state            | streaming
    sent_location    | 0/7000318
    write_location   | 0/7000318
    flush_location   | 0/7000318
    replay_location  | 0/7000318
    sync_priority    | 0
    sync_state       | async

This shows that the previously cloned standby (node2 shown in the field application_name) has connected to the primary from IP address 192.168.1.12.

From PostgreSQL 9.6 you can also use the view pg_stat_wal_receiver to check the replication status from the standby.

    repmgr=# SELECT * FROM pg_stat_wal_receiver;
    Expanded display is on.
    -[ RECORD 1 ]---------+--------------------------------------------------------------------------------
    pid                   | 18236
    status                | streaming
    receive_start_lsn     | 0/3000000
    receive_start_tli     | 1
    received_lsn          | 0/7000538
    received_tli          | 1
    last_msg_send_time    | 2017-08-28 15:21:26.465728+09
    last_msg_receipt_time | 2017-08-28 15:21:26.465774+09
    latest_end_lsn        | 0/7000538
    latest_end_time       | 2017-08-28 15:20:56.418735+09
    slot_name             |
    sender_host           | node1
    sender_port           | 5432
    conninfo              | user=repmgr dbname=replication host=node1 application_name=node2
   

Note that the conninfo value is that generated in postgresql.auto.conf (PostgreSQL 11 and earlier: recovery.conf) and will differ slightly from the primary's conninfo as set in repmgr.conf - among others it will contain the connecting node's name as application_name.