try like
DECLARE @BCPCmd varchar(8000)
SET @BCPCmd='BCP "DECLARE @colnames VARCHAR(max);SELECT @colnames = COALESCE(@colnames + ',', '') + column_name from RPIUser_input.dbo.INFORMATION_SCHEMA.COLUMNS where TABLE_NAME=PartSiteTrans; select @colnames;" queryout c:\export\HeadersOnly.csv -c -T -SRQL'
EXEC xp_cmdshell @BCPCmd,no_output
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SQL Server MVP
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