If the partnership sold an asset owned by the partnership, each partner's share of the capital gain will be reported on his K-1 form, like other partnership income and expenses. In Turbotax, all you have to do is enter the amounts from the K-1 as usual.
The income reported will increase your outside basis, and the cash distributed will decrease it. This is true for all types of income, not just a capital gain. But you don't have to report your outside basis anywhere on your tax return until you sell or otherwise dispose of your partnership interest - see next item.
If on the other hand you sold your interest in the partnership to a third party and realized a capital gain, you report the transaction on form 8949, like any other sale of a capital asset, such as shares of stock. You report the amount received as the sale price and your outside basis as the cost.
