I have a client that purchased a limited partnership investment in his IRA. the K1 from the LP shows UBTI. how does the client or IRA deal with this tax? my understanding is the IRA must pay the tax and it is at trust tax rates.

The trustee must file form 990T. There is a $1,000 UBI threshold above which a filing is required.
Depending on the state, there may be state filings required as well.
You are correct that the IRA plan must pay the tax.