If due to special reason you really want to choose "2 Provide wavefunction file of involved elements by yourself or invoke Gaussian to automatically calculate them", you should input path of Gaussian executable file in this stage, such as D:\study\g16w\g16.exe (or you can define the path via "gaupath" parameter in settings.ini file, then you do not need to manually input the path every time), then Multiwfn will invoke Gaussian to compute atomic .wfn files, which are needed in the calculation of Hirshfeld charges.

But during the calculation i find
"Multiwfn -- A Multifunctional Wavefunction Analyzer
Version 3.6, release date: 2019-May-21
Project leader: Tian Lu (Beijing Kein Research Center for Natural Sciences)
Below paper *MUST BE CITED* if Multiwfn is utilized in your work:
          Tian Lu, Feiwu Chen, J. Comput. Chem., 33, 580-592 (2012)
Multiwfn official website: http://sobereva.com/multiwfn
Multiwfn English forum: http://sobereva.com/wfnbbs
Multiwfn Chinese forum: http://bbs.keinsci.com/wfn
( The number of threads:  2   Current date: 2020-05-08   Time: 21:56:26 )

Please wait...
Loading various information of the wavefunction
The highest angular moment basis functions is D
Loading basis set definition...
Loading orbitals...
Converting basis function information to GTF information...
Generating overlap matrix...
Generating density matrix based on SCF orbitals...

Total/Alpha/Beta electrons:    100.0000     50.0000     50.0000
Net charge:     0.00000      Expected multiplicity:    1
Atoms:     18,  Basis functions:    209,  GTFs:    408
Total energy:   -1035.970153780311 Hartree,   Virial ratio:  2.00629841
This is a restricted single-determinant wavefunction
Orbitals from 1 to    50 are occupied
Title line of this file: 9Chloroflurociloquinol

Loaded C:\Multiwfn_3.6_bin_Win32\9Chloroflurociloquinol.fch successfully!
Formula: H5 C9 N1 O1 F1 Cl1
Molecule weight:       197.59350

                    ************ Main function menu ************
0 Show molecular structure and view orbitals
1 Output all properties at a point
2 Topology analysis
3 Output and plot specific property in a line
4 Output and plot specific property in a plane
5 Output and plot specific property within a spatial region (calc. grid data)
6 Check & modify wavefunction
7 Population analysis and atomic charges
8 Orbital composition analysis
9 Bond order analysis
10 Plot total DOS, partial DOS, OPDOS, local DOS and photoelectron spectrum
11 Plot IR/Raman/UV-Vis/ECD/VCD/ROA spectrum
12 Quantitative analysis of molecular surface
13 Process grid data (No grid data is presented currently)
14 Adaptive natural density partitioning (AdNDP) analysis
15 Fuzzy atomic space analysis
16 Charge decomposition analysis (CDA) and extended CDA (ECDA)
17 Basin analysis
18 Electron excitation analysis
19 Orbital localization analysis
20 Visual study of weak interaction
21 Energy decomposition analysis
100 Other functions (Part1)        200 Other functions (Part2)
7//

                 ============== Population analysis ==============
-2 Calculate interaction energy between fragments based on atomic charges
-1 Define fragment
0 Return
1 Hirshfeld atom population
2 Voronoi deformation density (VDD) atom population
5 Mulliken atom & basis function population analysis
6 Lowdin atom & basis function population analysis
7 Modified Mulliken atom population defined by Ros & Schuit (SCPA)
8 Modified Mulliken atom population defined by Stout & Politzer
9 Modified Mulliken atom population defined by Bickelhaupt
10 Becke atomic charge with atomic dipole moment correction
11 Atomic dipole corrected Hirshfeld atomic charge (ADCH) (recommended)
12 CHELPG ESP fitting atomic charge
13 Merz-Kollmann (MK) ESP fitting atomic charge
14 AIM atomic charge
15 Hirshfeld-I atom population
16 CM5 atomic charge
17 Electronegativity Equalization Method (EEM) atomic charge
18 Restrained ElectroStatic Potential (RESP) atomic charge
1//
Citation: Theor. Chim. Acta. (Berl), 44, 129-138 (1977)
This task requests atomic densities, please select how to obtain them
1 Use build-in sphericalized atomic densities in free-states (more convenient)
2 Provide wavefunction file of involved elements by yourself or invoke Gaussian
to automatically calculate them
2
Running: rmdir /S /Q wfntmp
Running: mkdir wfntmp
Note: Some or all atom .wfn files needed are not present in "atomwfn" folder, t
hey must be calculated now. See Section 3.7.3 of the manual for detail.
Now please input the level for calculating atom wfn files, theoretical method i
s optional.
For example: 6-31G* or B3LYP/def2SVP    You can also add other keywords at the
same time, e.g. M062X/6-311G(2d,p) scf=xqc int=ultrafine
6-31g*
Could not find Gaussian path defined in "gaupath" variable in settings.ini

Input the path of Gaussian executable file, e.g. "D:\study\g16w\g16.exe"
In this stage I am unable to follow the required instruction to define gaupath. I have asked Gaussian, they told me this may be the requirement of “Multiwfn”
=====================
After you select subfunctions -1 or -2 to study promolecular and deformation properties, Multiwfn checks whether .wfn files of all elements involved in present system have been presented in “atomwfn” subdirectory of current directory, if not, Multiwfn automatically invokes Gaussian to generate the missing element .wfn files and sphericalizes their densities. If the path of Gaussian executable file (“gaupath” parameter in settings.ini) is incorrect or has not been defined, Multiwfn will ask you to input the path of Gaussian executable file. (but how?)

Waiting for reply, With sincere thanks,
partha

If you are not familiar with Multiwfn, I strongly suggest you first reproduce relevant examples in Chapter 4 of Multiwfn manual. If you can normally reproduce the example, it is highly possible that your input file is problematic.