I feel bored to have this in my all mails 'Please let me know if any questions/comments', any best alternate sentence would be helpful for me
You can use @Amadeus' answer or one of the following:
"Any questions or comments are welcome"
"Feel free to leave questions or comments"
"Questions or comments are appreciated"
If your standard email encourages an ongoing dialogue, you can add 'further' to the line:
- "If further questions should arise, do feel free to ask."
There are many ways to say it. Say whatever you feel best suits