Hello Dylan,
Thank you for writing to us today. You could use the campaign_criterion resource to retrieve the list of all the negative keywords set at the campaign level by specifying the campaign_criterion.negative field to true in your report query. Please find below the sample report query to list all the negative keywords set at campaign level. Let us know if you need any additional information.
"SELECT campaign_criterion.keyword.text FROM campaign_criterion WHERE campaign_criterion.negative = TRUE"
Regards,
Nikisha Patel, Google Ads API Team