exposing spam confidence level in Exchange

Is there a way to expose the SCL of the messages in the Archive Folder, OWA or Outlook?

Yes, it's possible. You need to create the following registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\ContentFilter
To archive the SCL rating with archived messages

1. In Registry Editor (regedit), right-click ContentFilter, click New, and then click DWORD value.
2. Type ArchiveSCL for the registry key value.
3. Right-click ArchiveSCL, and then click Modify.
4. In Edit DWORD, under Value Data, type 1.
5. When this registry key value is set to 1, Intelligent Message Filter saves the SCL rating with the archived messages. The SCL rating is persisted in the message as an extended message header (X-SCL).

When this registry key is set to 0, or if the registry key value does not exist, Intelligent Message Filter archives the message, but does not save its associated SCL rating.

Now, your messages are receiving have an X-SCL message header with SCL Level. Then, you can see SCL in Archived Folder, Outlook and OWA.

For exposing SCL in Outlook or OWA, see below:
Exposing SCL in Outlook
Exposing SCL in OWA
Microsoft Exchange Intelligent Message Filter Deployment Guide