library(tidyverse)

# x is a grouped tibble, my_col is the column to peel
my_function <- function(x, my_col){

    my_col_enc <- enquo(my_col)

    # Trying to grab the groups and then peel off the column
    x_grp <- x %>% group_vars()
    excluded <- x_grp[!is.element(x_grp, as.character(my_col_enc))]

    # My calculations are two-tiered as described in the original description
    # simplifying for example
    x %>% group_by(excluded) %>% tally()

}

# This should be equivalent to mtcars %>% group_by(gear) %>% tally()
mtcars %>% group_by(cyl, gear) %>% my_function(cyl)

library(tidyverse)

  my_function <- function(x, my_col){

    my_col_enc <- enquo(my_col)

    # Trying to grab the groups and then peel off the column
    x_grp <- x %>% group_vars()

    # here, make sure this is a symbol, else it'll group as character later (e.g. 'gear')
    excluded <- rlang::sym(x_grp[!is.element(x_grp, as.character(my_col_enc))])

    # need to use !'s to deal with the symbol
    x %>% group_by(!!excluded) %>% tally()
  }