I use Operator - "is one of (,-separated values)" 1,2,3,4,5,6,7,8
That operator is stating the following.
FIELD_VALUE is one of the following COMMA_SEPARATED_VALUES
This means if the field value is "Test" and you have "Test,Pass,123" it'll pass because "Test" is one of the values to match.
But problem if user selected two or more values in "cb_interests" field, in search by only one of this values user not show.
That's due to the way multiselect fieldtypes store their values. They're stored as VALUE_1|*|VALUE_2|*|VALUE_3 etc.. So when you do an equal to operator like "is one of" it's comparing "VALUE_1|*|VALUE_2" is one of "1,2,3" and is always going to fail. You've 3 options basically. You can use the "Contains" or "Does not nontain" operators and match against a single value (e.g. FIELD Contains 1) or use the "Is REGEXP" or "Is Not REGEXP" operators and supply the the appropriate SQL safe REGEXP to match your values. The final option is set it to Advanced and supply your own SQL.
2. In Sorting tab I sort users by "cb_featured" field. But there is only two options "Descending" and "Ascending".
How I can sort users also by the positions?
It simply adds that field column to the Order By statement of the query, which it can only do so in Ascending or Descending order. If you need an advanced usage you need to set it to Advanced and supply your own Order By SQL.