You can use R packages tidyr and dplyr for this.

# First import into R
table.file <- read.table("your.file.txt", header = T, sep = "\t", stringsAsFactors = F)

library(tidyr)

# Get your genes in separate rows
table.genes.sep <- separate_rows(table.file, Submitted.entities.found, sep = ";")

library(dplyr)

# use dplyr to count genes and sort
table.genes.count <- table.genes.sep %>% count(Submitted.entities.found, sort = TRUE)

Something like this, which will display most frequent 10 gene names:

head(names(table(unlist(strsplit(table.file$Submitted.entities.found, sep = ";")))), n = 10)