In 1936? Largely the entire population. The terror of 1937 or "Yehozchina' even though that term is inaccurate, and the continued terror in 1938 was where your average Joe was most likely in danger. In 1936 the purge was still the show trials, torture, and execution of the Nomenklatura, or communist party elite. There were trials like the Shakhty and Industial party trial did occur against those who weren't exactly members of the elite, these were still political trials and therefore are still party cleansing rather than a terror against the population.

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So really anyone who wasn't considered a political threat to the regime or wasn't a high level elite could be considered safe in 1936.

Assuming you confused 1937 with 1936 then the answer changes alot. Like seriously alot. Yehozchina killed hundreds of thousands. Once again I may remind you that Yehoz was obviously deeply involved in the terror, and even had some autonomy, but there is no evidence that he did these things without Stalin's approval, but that is something for another question.

In 1937 the elite were still targeted, the infamous army purge occurred in 1937. There was more show trials obviously, and more torture and executions. In terms of the general population, there was a lot more potential victims. Peasants were killed in mass operation such as Order 00447 or "Document 170" in my source which had 55,450 people ordered to be executed. Poles, Germans, Latvians, and other ethnic groups were targeted. Overall the regime had anyone who wasn't a low Russian industrial worker considered a threat in 1937.

In summary in 1936 your average Joe was safe from the elite party cleansing but by 1937 the purges had become a general terror on the "Anti-Soviet elements" and many more peoples, like the peasantry, lower party members, and ethnic minorities became targets.

Source used "Road to terror" by J. Arch Getty