Self employment earnings on a sole proprietor is computed as net earnings from a Schedule line 31 then multiplied by 92.35% to get to the self employment earnings subject to SE tax. A Schedule K-1 from From a partnership (Form 1065) should indicate what your self employment earnings are on Box 14. That comes from the partnership's income or loss for the year. You may or may not have access to the detail if it's coming from a partnership where you do not have access to the records.
The mileage and other expenses should be accounted in the partnership if understand you correctly. Clearly some of these issues are better handled by a CPA or EA that can help with the tax return.
