It's not currently possible to see what records were skipped during import. Here is a workaround to see what records did not make it. We realize this is a long workaround and apologize. If you would like this feature, please make a feature request here.
1. Filter your records by its import tag. To see the import tags, go to settings -> import data -> find the file that imported -> click summary -> copy the tag
2. Go back to your records -> filter your records by the copied tag -> click the three dots to export the list
3. Import the Excel download to a Google sheet:
4. Find the file you originally imported
5. Make another tab in the sheet and copy/paste your import
6. Use this tool, to highlight all the duplicates, by selecting "Compare columns or sheets" as above. You will see which ones are not highlighted and then you will know which ones didn't make it: https://copper.zendesk.com/hc/en-us/articles/213584103-How-do-I-look-for-duplicates-