OK. It took 5 hours for chkdsk to run. Whew. But improvement in performance is already amazing. What's next? I'm pasting the report below.
For future reference, how often do you recommend I run chkdsk as routine maintenance? Monthly? & what "red flags" would I be looking for in the event report?
But, FYI,here's what the Event Viewer looks like to me--a little different from your instructions, but I managed to get the report.

I didn't get this instruction at first:
- In the left panel, expand Windows Logs and then click on Application
For my notes for next time I've added "(below it, still in the left panel). (If you click in the right panel you need to also click “open” to see what’s next.)"
HERE'S THE EVENT REPORT:
Log Name: Application
Source: Microsoft-Windows-Wininit
Date: 10/13/2015 12:45:58 PM
Event ID: 1001
Task Category: None
Level: Information
Keywords: Classic
User: N/A
Computer: Laptop1
Description:
Checking file system on C:
The type of the file system is NTFS.
Volume label is OS.
A disk check has been scheduled.
Windows will now check the disk.
Stage 1: Examining basic file system structure ...
Cleaning up instance tags for file 0x89ad.
311552 file records processed.
File verification completed.
5911 large file records processed.
0 bad file records processed.
Stage 2: Examining file name linkage ...
406342 index entries processed.
Index verification completed.
0 unindexed files scanned.
0 unindexed files recovered.
Stage 3: Examining security descriptors ...
Cleaning up 1873 unused index entries from index $SII of file 0x9.
Cleaning up 1873 unused index entries from index $SDH of file 0x9.
Cleaning up 1873 unused security descriptors.
CHKDSK is compacting the security descriptor stream
Security descriptor verification completed.
47396 data files processed.
CHKDSK is verifying Usn Journal...
Usn Journal verification completed.
Stage 4: Looking for bad clusters in user file data ...
311536 files processed.
File data verification completed.
Stage 5: Looking for bad, free clusters ...
100790593 free clusters processed.
Free space verification is complete.
CHKDSK discovered free space marked as allocated in the volume bitmap.
Windows has made corrections to the file system.
No further action is required.
473900031 KB total disk space.
70194208 KB in 234245 files.
149868 KB in 47399 indexes.
0 KB in bad sectors.
393579 KB in use by the system.
65536 KB occupied by the log file.
403162376 KB available on disk.
4096 bytes in each allocation unit.
118475007 total allocation units on disk.
100790594 allocation units available on disk.
Internal Info:
00 c1 04 00 30 4c 04 00 68 5d 08 00 00 00 00 00 ....0L..h]......
3d 08 00 00 58 27 00 00 00 00 00 00 00 00 00 00 =...X'..........
Windows has finished checking your disk.
Please wait while your computer restarts.
Event Xml:
<Event xmlns="
http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name="Microsoft-Windows-Wininit" Guid="{206f6dea-d3c5-4d10-bc72-989f03c8b84b}" EventSourceName="Wininit" />
<EventID Qualifiers="16384">1001</EventID>
<Version>0</Version>
<Level>4</Level>
<Task>0</Task>
<Opcode>0</Opcode>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2015-10-13T16:45:58.000000000Z" />
<EventRecordID>61074</EventRecordID>
<Correlation />
<Execution ProcessID="0" ThreadID="0" />
<Channel>Application</Channel>
<Computer>Laptop1</Computer>
<Security />
</System>
<EventData>
<Data>
Checking file system on C:
The type of the file system is NTFS.
Volume label is OS.
A disk check has been scheduled.
Windows will now check the disk.
Stage 1: Examining basic file system structure ...
Cleaning up instance tags for file 0x89ad.
311552 file records processed.
File verification completed.
5911 large file records processed.
0 bad file records processed.
Stage 2: Examining file name linkage ...
406342 index entries processed.
Index verification completed.
0 unindexed files scanned.
0 unindexed files recovered.
Stage 3: Examining security descriptors ...
Cleaning up 1873 unused index entries from index $SII of file 0x9.
Cleaning up 1873 unused index entries from index $SDH of file 0x9.
Cleaning up 1873 unused security descriptors.
CHKDSK is compacting the security descriptor stream
Security descriptor verification completed.
47396 data files processed.
CHKDSK is verifying Usn Journal...
Usn Journal verification completed.
Stage 4: Looking for bad clusters in user file data ...
311536 files processed.
File data verification completed.
Stage 5: Looking for bad, free clusters ...
100790593 free clusters processed.
Free space verification is complete.
CHKDSK discovered free space marked as allocated in the volume bitmap.
Windows has made corrections to the file system.
No further action is required.
473900031 KB total disk space.
70194208 KB in 234245 files.
149868 KB in 47399 indexes.
0 KB in bad sectors.
393579 KB in use by the system.
65536 KB occupied by the log file.
403162376 KB available on disk.
4096 bytes in each allocation unit.
118475007 total allocation units on disk.
100790594 allocation units available on disk.
Internal Info:
00 c1 04 00 30 4c 04 00 68 5d 08 00 00 00 00 00 ....0L..h]......
3d 08 00 00 58 27 00 00 00 00 00 00 00 00 00 00 =...X'..........
Windows has finished checking your disk.
Please wait while your computer restarts.
</Data>
</EventData>
</Event>