PureEngage On-Premises

two SIP Server deployed, Endpoint registered SipServer2 (with same DN number)
and inbound call received SipServer1
dr-forward options set 'oos'
but SipServer1 generated only '404 not found' 
how to forward call to SipServer2 ?

Are you sip endpoints configured to enable the DR funcionality? What say SIP server log? I assume you have license for DR :)

For Lab test,
in case of network issue, endpoint registered only dr peer2, inbound call receives dr peer1, 
can it forward calls to dr peer2?

14:51:56.294: SIPTR(32): Step 0 - SipTransactionCreateCall(33) complete
14:51:56.294: SIPTR(32): Begin step 1 - SipTransactionResolveCallInfoByDialPlan(34)
14:51:56.294: DialPlan: No dialplan defined for 01011112222.
14:51:56.294: DialPlan: No rule applied, using original destination '3001'.
14:51:56.296: DialPlan: clear flag 0x100, callId 16778224
14:51:56.300: Number: 3001 : checking for a softswitch configuration
14:51:56.300: Number:3001 did not find any softswitch with matching prefix to send this call to
14:51:56.300: Unable to resolve number for DN:3001
14:51:56.300: SIPDM: failed to get registration info for 3001
14:51:56.300: SIPDM: failed to get registration info for 3001
14:51:56.300: Call connect failed with error WRONG_NUMBER, no DialPlan script condition - rejecting call.
14:51:56.300: SIPTR(34): complete
14:51:56.300: SIPTR(32): Step 1 - SipTransactionResolveCallInfoByDialPlan(34) complete
14:51:56.300: SIPTR(32): Begin step 2 - SipTransactionRejectCall(35)
14:51:56.300: GetRegistration::Unable to resolve number for DN:dummy
14:51:56.300: GetRegistration::Unable to resolve number for DN:dummy
14:51:56.300 SIPCONN(01011112222): re-invite-called-initiated
14:51:56.302: Sending  [0,UDP] 327 bytes to 172.168.1.20:5060 >>>>>
SIP/2.0 404 Not Found^M
Via: SIP/2.0/UDP 172.168.1.20;branch=z9hG4bKac830556352;received=172.168.1.20^M
From: <sip:01011112222@172.168.1.20>;tag=1c830547021^M
To: <sip:3001@s1sip.nhis.com;user=phone>;tag=00226D52-2CD9-1899-8E95-4B01A8ACAA77-9252^M
Call-ID: 8305459572711201315737@172.168.1.20^M
CSeq: 1 INVITE^M
Content-Length: 0^M
 

It seems your SIP peers for DR function is not configured properly. Try to check the guide step-by-step and going through again to ensure that all necessary steps were done

Thanks for Jakub. 
where to find related documents? 
are you meaning SIPServer HA Deployment Guide? fully configured in this guide
i need some more detailed guide