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Also note that resume (checkpointing) functionality will not work if you remove the work OR .nextflow directory for a given workflow execution location - it will think you are starting over from the beginning. You will see the following message:
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Each workflow execution will generate a .nextflow.log file in the directory where the pipeline is invoked. Subsequent executions will result in nextflow renaming previous .nextflow.log files to .nextflow.log.1, .nextflow.log.2, etc., depending on how many executions are performed in the current directory - .nextflow.log is always going to be the log file associated with the most recent run, with files with increasing numbers associating with older and older runs (.2 happened before .1, etc.).
Workflows that are resume-d will generate a NEW .nextflow.log file, so it may be necessary to reconcile the newest log with the most recent previously generated logs to view full workflow output.
Some workflows may also include a debug profile, which you can invoke alongside other profiles, to get more verbose output while the workflow is executing.