The pKa is equal to the same number as the pH when 50% of the alkaloid is in salt form and 50% is freebased. The pH and pKa at which this occurs for DMT is 8.68. I.e., the pKa=8.68 and the pH=8.68.
At pH 6.68 (pKa minus 2) 1% is freebased and 99% is salted At pH 7.68 (pKa minus 1) 10% is freebased and 90% is salted At pH 8.68 (pKa +/- 0) 50% is freebased and 50% is salted At pH 9.68 (pKa plus 1) 90% is freebased and 10% is salted At pH 10.68 (pKa plus 2) 99% is freebased and 1% is salted
It’s not completely accurate to go by just the pKa of an alkaloid. There are other factors at play such as solubility of the various salts and the solubility of the freebased compound.
The solubility of various alkaloid salts differ from the solubility of each other and their parent freebase form. For example, DMT freebase is almost insoluble in water while DMT fumarate is water soluble but much less water soluble than DMT acetate; mescaline freebase is water soluble while mescaline sulfate is less water soluble and mescaline hydrochloride is highly water soluble, etc.