Where can I get ?or how can I make a mappability track for hg38 assembly

Lucky you @manojmumar_bhosale I worked on similar problem recently and therefore have the bash script you can use.
Required tools:

1. GEM libary from here

2. UCSC’s wigToBigWig from here (I chose binary for Linux 64 bit, you can choose different OS)

   #!/bin/bash - 
   #===============================================================================
   #
   #          FILE: mappa_cacl.sh
   # 
   #         USAGE: ./mappa_cacl.sh 
   # 
   #   DESCRIPTION: 
   # 
   #       OPTIONS: ---
   #  REQUIREMENTS: ---
   #          BUGS: ---
   #         NOTES: ---
   #        AUTHOR: Vang Le (vql AT rn.dk) 
   #  ORGANIZATION: 
   #       CREATED: 26/02/16 01:49
   #      REVISION:  ---
   #      Reference: http://wiki.bits.vib.be/index.php/Create_a_mappability_track
   #===============================================================================
   
   set -o nounset                              # Treat unset variables as an error
   
   pref="rn6.softmask.all" # should be changed
   reference="rn6.softmask.all.fa" # should be changed
   idxpref="${pref}_index"
   thr=20; # use 20 cores, change it to the number you want to use
   outmappa="rn6.mappa.tsv" # should be changed
   #make index for the genome
   gem-indexer -T ${thr} -c dna -i ${reference} -o ${idxpref}
   
   # The following calculates index and creates mappability tracks with various kmer lengths.
   # it may take long time to finish.
   # choose the right kmer length for you.
   for kmer in 45 50 75; do
   
     # compute mappability data
      gem-mappability -T ${thr} -I ${idxpref}.gem -l ${kmer} -o ${pref}_${kmer}
     mpc=$(gawk '{c+=gsub(s,s)}END{print c}' s="!" ${pref}_${kmer}.mappability)
     echo ${pref}_${kmer}"t"$mpc >> $outmappa
     # convert results to wig and bigwig
     gem-2-wig -I ${idxpref}.gem -i ${pref}_${kmer}.mappability -o ${pref}_${kmer}
     wigToBigWig ${pref}_${kmer}.wig ${pref}.sizes ${pref}_${kmer}.bw
   
   done
   

Script from @biocyberman is great. For those who are still looking for this, here are steps:

1) Get the reference hg38 genome, in uncompressed fasta format (obviously)

2) Get the ‘gemtools’:
a) SourceForge –> Version 2, pre release
or
b) GitLab –> Version 1.7

3) Create the index of the genome by using following command:

gemtools index -i <referenceGenome.fasta:PATH> -t <NumberOfThreadsToUse:int>     
e.g.:
gemtools index -i GRCh38.p12.fasta -t 40

4) Once, the index is made, generate the mappability data like:

gem-mappability -I <referenceGenome_index.gem:PATH> -l <K-mer_length:int> -o <output_name.gem:PATH>
e.g.: For 100 mer, the command will be:    
gem-mappability -I GRCh38.p12.gem -l 100 -o GRCh38_mappability_100mer.gem

The complete guide is available at this wiki