single owner llc received k-1 from partnership where to report on his 1040

I can help with this part: "If the client has (s) corporation. He will report the K-1 directly under his (s)."

Nope. But, on the other hand, if the S Corp is the partner in the Partnership that issued the K-1, then the Corporation is the Partner and reports on the Corporate return, which is the 1120S, which generates its own K-1 to the Shareholder(s). Then, the Shareholder(s) use that K-1 for their own 1040 requirements.

"But if he has guaranteed payment on his k-1 received, how is that will report under (s)"

Perhaps you have not confirmed exactly "who" is the partner in that partnership?

Your client that has a single-member LLC is running their own business (the Sched C) as a disregarded entity, which means Self. They, the person, has the Sched C business. If they, the person, is the partner in that other partnership, then They, the Person, reports it on their individual tax return, which makes it part of the 1040. Their business that gets reported on Schedule C, is not separate from Them. You know this, because the Schedule C is a part of Form 1040. There is no Schedule C that is part of Form 1120S, for instance.

"and what about the self-employment tax on it?"

Read the instructions: https://www.irs.gov/pub/irs-pdf/i1040sse.pdf